Welcome to the Q&A Forum

Google officially said the site speed is a SEO factor which, when implemented, will affect 1% of SERP results. This gives some idea of the scope of it's relevancy. (not saying 1% is either high or low, this is all very subjective)

Having said that, beyond speed improvement, CDN provides other SEO related benefits.

I've actually just published a 2-part Blog post that investigates SEO & CDN related myths and talks about CDN and SEO benefits, I hope you`ll find it useful. it should answer all questions:

Part 1: SEO & CDN Myths
Part 2: SEO & CDN benefits

I absolutely agree with Vadim. (+1)

Google is the best source for Google facts. Everything else is just speculation.

And yes, generally speaking, the best answer is to use a CDN.... 
The reason is simple. CNDs proxy technology, which was designed to minimize "physical" distances between the site's content and browsers, directly influences TTFB.

Being an in-house SEO for a CDN company I get a lot of questions about this from our support and clients. I have to admit, until recent Moz post, I wasn't aware of full implications of TTFB and considered it to be one of few page load speed related metrics.  (http://moz.com/blog/how-website-speed-actually-impacts-search-ranking)

This post really helped me get a better grasp on things. Interestingly enough, few month ago one of our clients Guest Posted in our blog about speed improvement gained by our free plan. Among other things, he mentioned 70% improvement in TTFB (grade going from F to A) 
(http://www.incapsula.com/the-incapsula-blog/item/718-what-incapsula-free-did-for-my-site)

At the time I didn't give it much attention. Because, like many others, I was focusing on overall load speeds.... 
Now I can't help but feel that this was a missed opportunity.
This post could be even better with the added SEO angle...
If anyone here is interested in giving this a try and guest posting about it, I`ll be happy to provide all resources needed on our end.

This is an issue I`ve dealt with over and over again for Joomla sites.

I had some good results with Canonical URL Module but didnt use it yet for 2.5 so Im reluctant to suggest it.

Im currently working with our Dev. Team to solve this for K2 - as far as I know, if you are a K2 user youll need a custom solution.

(yes Im aware of K2 canonical plugin and no, I dont recommend it)

GL

(+1)  For redirect to main category page option. I did this several time, including for a very large tourism site which had a LOT of "inventory" changes (we are talking about dozens-hundreds/day) and had great results.

One thing I would like to suggest is to look into doing 302 and removing the redirects after 2-3 month.

The reason for this is purely practical. In our case, after just a few month, we were looking at many thousands of redirects and this is not something you want to "carry around".
My suggestion allows you to still make use of link juice for removed pages and, at the same time, have a manageable redirect profile.

As a safe net you can have a generic: "404 >>> 301 >>> Homepage" rule underneath.

These are pretty "strong" domains we are talking about with enormous link profiles, tons of social signals, a lot of visits etc.. You can probably "beat them" at some niche KW, but this will take some work.
This is somewhat like competing  against Wikipedia, which dominates a lot of niche KW and some major KW too...
As to your second question, permanent links will provide permanent value.

Oleg gave a great answer.

Still I would add 2 things here:

1. Go to GWMT and under "Health" do a "Fetch as Googlebot" test.
     This will tell you what pages are reachable.

2. I`ve saw some occasions of server-level Googlebot blockage.
If your robots.txt is fine and your page contains no "no-index" tags, and yet you still getting an error message while fetching, you should get a hold on your access logs and check it for Googlebot user-agents to see if (and when) you were last visited.

This will help you pin-point the issue, when talking to your hosting provider (or 3rd party security vendor).

If unsure, you can find Googlebot information (user agent and IPs ) at Botopedia.org.

Putting a noindex/nofollow on an index url will remove it from SERPs, although some ulrs will still show for direct search (using the url itself as a KW) but even then they will appear as clear links without any TItle/Description details.

Using a 301 redirect will remove the old page from index, regardless of noindex/nofollow.

If you are using a noindex/nofollow for the new url - both will not show.

Not necessarily.  Can you provide a link to Google SERP so I can answer this accurately?
Sometime (pretty often) Google will show one page but provide the rankings due to another page.

For example, I have a strong "CCTV Cameras" category page and under I have a "[Specific Type of CCTV Camera] " page. The first page is strong and he will provide me with high ranks but it dosen't mean it will be show for it. Instead, due to visitor data or/and social signals, the second page may appear if it's temporarily more popular.

After it gets removed (i.e. sold out) the first page, or other trendier topic related page, will assume the position.

This scenario can be discovered by looking at 100 results (use. advance search) there sometimes youll find several results from the same site, side by side - where in basic search youve saw only one single result. This is a symbiotic relationship I`m talking about. The 1st and displayed result is not the "cause" for high rank, it just "riding co-tails" of other strong pages.

From what you`ve described, you see some of these too ( " take over 1 or more of the page one results in my niche...") For these, if the 1st page gets removed, another will probably take its place...

Hi Vadim

Thanks.
Yep, I work for Incapsula but no, we are not the said "Mod".  

As for CF comparison... Generally speaking, we are more business oriented and security focused. I know that our security offering is more comprehensive, especially because both WAFs were comparatively pen-tested on several occasions and we always came out as consistently (and significantly) better option.We also have addition security features - like 2FA support and backdoor shell protection - which CF simply doesn't offer and we do more in way of ddos mitigation, especially against smart application layer attacks which require security capabilities, besides network muscle.

Still, speed wise, I always considered us to be pretty much on the same level. However, until few days ago I never considered TTFB to be such core SEO factor, so maybe we have better performance there...  
But again, to be fair, I`m only speculating - mostly based on the CF blog you've shared.
(if TTFB is considered un-important, it might also be under developed...)

Might be an interesting thing to test and document.

Hi

I`m not sure if this is the best way to go about it.

Robots.txt is commonly used for folder level disallow rules, I`m not sure how it will respond to parameters.

Having said that, there are several things you can do here:

1. You can use WMT to zero in on this parameter and  prevent it from being searched.
To do so choose Configuration>>URL Parameters, answer "Yes" to the question about content change and  
    check-in the 3rd bullet (Only URL with value...) Of course you'll need to choose "1" as the right value.

2. If this still didn't solve your issue, you might want to try using htacess + regex to prevent access by user agent.
    You can find user-agent information here Googlebot user agent list

Also, you may want to check my blog post  about some of the less known Googlebot Facts (shameless self-promotion)

Best

Igal

Honestly, I don't know. I don't think TTFB was ever comparatively tested - at least no to the best of my knowledge.

For security, these are some of the resources I can point to.
I understand that this is not the main issue
Still, I wanted to provide some factual context to my previous statements.
http://zeroscience.mk/files/wafreport2013.pdf http://ddos-protection-services-review.toptenreviews.com/ http://tonyonsecurity.com/2012/11/13/protecting-your-website-cloudflare-or-incapsula/ 
(This last one is interesting since Tony is a COO of Sucuri. Some would call his our competitor. I prefer 'colleague' )

Didn't say it wasn't.

I`m just not sure how these rules apply to parameters, since they are not a part of the "core" URL.

(For example: What happens if I take a URL from your site, change a nocrawl=1 to nocrawl=0 and link to it from mine?
Do you have any URL sanitation rules in place to overcome that or will the page be indexed by Googlebot when it crawls my site and moves on to yours?)

Personally, when dealing with parameters, I find it easier to work with WMT so I was offering an easier workaround, (at least for me)

To tell you the truth, I would use hard-coded on page meta noindex/nofollow here (again, as parameters can be so easily manipulated).

Hi
SEO wise, there are many things to consider before on-boarding a CDN service and bot filtering is one of them.
I've covered the topic in 2 blogs posts about a year ago:

1. CDN's SEO related advantages 2. CDN's SEO related myths (and possible issues to consider)

PS: I work for CDN-based security and acceleration service provider - Incapsula.

Generally speaking, CAPTCHA based DDoS protection is not advised as it will drive away clients and DDoS bots alike.
Same goes for delay pages.

Also, DDoS attacks are swift and can bring site/server down in minutes so the manual approach is risky and probably less effective than it sounds on paper. Even if you are always near your PC, like many of us here are, you`ll still be exposed on weekends, nighttime, launch breaks, etc... Hackers know that and will exploit it. (favorite attack time - VERY EARLY Sunday mornings... )

You should also consider that DDoS can serve as a means to an end. It's often used to "soften" the protective layer to hack the database, inject the site with backdoors, deface or delete it and so on and so forth.

What you really need is a combination of auto-triggering and transparent mitigation, which shies away from intrusive mitigation methods in favor of more subtle progressive challenges (i.e. JS challenge combined with reputation and behavior monitoring).
This may sound fancy but it really this is the emerging industry standard and growing competition between vendors actually drives costs down.