Quite simply, you can't access someone else's analytics data.  Well, not without their username and password, or an extremely talented hacker, at least.

There are a few ways (think Alexa) you can estimate traffic - some of them are better than the rest, but all of them are imperfect.  When you compare a website to another and use these metrics in a relative sense, however, they can be useful.  Try looking up the estimated search volume of a competitors' brand names compared to your brand name using the Google Keyword Tool.  This won't give you an accurate traffic estimate, but it might just help you figure out who's getting the most traffic and where your website falls in the market.

Will it cause harm?  Not likely.  If Google suspects the links aren't kosher, it will probably just ignore (or "devalue") the links.

As to whether it is a shady or manipulative practice - debatable.  From my perspective, I don't quite see how it is all that different from a company linking to its partners, suppliers, or customers.  The link represents a business relationship, and that relationship has value.  If I have a client in the position to get these kinds of links, for me it's a no brainer - get 'em.  At the very worst, they have no impact SEO-wise, but help with branding and referral traffic.  Google's perspective may differ.

As to why the practice might not be working out so well for you - do you run linkbuilding campaigns for the websites you develop?  Does anybody?  Do many of the websites share a C class address?

A bunch of links from websites with weak backlink profiles or the same C class addresses won't take you very far.

BONUS - a few linkbuilding tactics guaranteed to work:

• Submitting your website to high quality, relevant directories
• Running a guest blogging campaign on a number of influential web design blogs
• Creating TRULY engaging and unique content and promote it via social media

I agree with Gianluca.  I think having a keyword-rich Twitter handle has extremely limited value, whereas conversely, a Twitter handle with your brand can have a ton of upside.

Yes, this will be seen as duplicate content.  There's no "easy" way to create unique content for each locale.  The best you can do is have a general outline and outsource the content creation to a high quality writer (or sit down and start writing yourself).  Article spinning or cheap writers will lead to low quality articles that will be difficult to get to rank well.

I think you should check this article out by Rand Fishkin.  He goes into detail about some companies in very BORING industries that have managed to develop incredibly successful link bait.

Probably not.  I've tried it all, from paying for social bookmarks to just submitting content and hoping for clicks.  What I've found is that if your content is truly quality, it's not going to need links to pick up steam and get shared.  A little nudge to your Twitter followers should be sufficient.  If an article sucks, buying 100 thumbs ups or diggs isn't going to really get it any exposure.  These things tend to balance themselves out - high quality content always rises to the top.

Ah, gotcha.  In my experiences dealing with SMB clients, some great links for local businesses are from:

• Local directories (these also help build citations for local SEO purposes)
• Guest blogging on industry-related blogs (in your author bio, you can include a link back to your Wisconsin Cheese company - or whatever business it is that you are promoting)
• Sponsoring local events or finding other ways to get your company local press (links from newspaper websites, press release websites, and charity/event websites)

I don't mean to steer you away from link exchange requests as a tactic.  It can certainly be useful, and you're right, it can be an easy method for small businesses to obtain links from other local companies or websites.  I just get frustrated by the low response rate  and oftentimes relatively weak link opportunities that I see with this tactic.  Usually local competitors' websites are just like your own before you start working on SEO - weak, unoptimized, and with few backlinks.

I'd rather spend my time to get a guest post published on an authoritative website in my industry.  It might not be as relevant of a link as one of my competitors in the area, but I can guarantee that it is going to have a ton of authority and link juice behind it.

I don't really do any formal reciprocal link exchanges via e-mail, but I do have a ton of success with the following method:

1.) Write a great blog post or piece of content for your own website.  Include in it links to other great blogs or resources about the topic you're writing about.

2. When the post is published, Tweet at the people whose websites you linked to and let them know that you mentioned their amazing, helpful resource in your latest post.

3. This generates a TON of retweets, and once in a while a great link back to my website from the blog/website that I mentioned.  It also helps me establish a line of communication with authoritative figures in my industry.  In short order, it puts me on their map, making future link requests much easier.

I know this isn't exactly what you're looking for, but I thought you might find it interesting.  Just my $0.02!