With Google traffic estimator / keyword Tool you get the data from the SE itself.

Which is all the more reason not to trust it!

if you don't have data for long tail keywords that is probably because the search for those terms is very low as far as volume.

Because Google only now reports on keywords that make them money

There can't / won't be another better source for this kind of data.

Your own analytics are the only thing that will give you a truly accurate data set, however I appreciate that it's not predictive for the most part For future reference as well, once you have top rankings for something always compare it against what you thought you would get and judge for yourself how accurate the tool is.

Anyway, yes, use the tool it's still one of the best resources you have access to.

How similar is the content?

I'm pretty sure you're not going to pass any link juice or authority to the new page using a canonical tag, especially if it has different content; it's just not a great way to fix anything.

Useful if the URL changes depending on how you end up at a destination page, but if you just happen to have 2 different pages about 'widgets' then sharing a canonical tag between them won't do too much.

Can you give me an example of what it is you're actually doing and why you think the pages should be the same? (I'm just not getting the impression they are the same page, sorry if I'm wrong)

If you've made an entirely new page with the same content and it's in the one location and you can change all your links to look there, then 301 the old page to the new page, don't just use rel=canonical.

If you've added a new category, so the old page was, for example, site/colour/product and you now allowed navigation like site/shape/product, then you may want to change the canonical tag if the 'shape' route into the page is the new "official" page.

Technically no, Google will only crawl pages that are publically available.

However, you could use their first click free feature - http://www.google.com/support/webmasters/bin/answer.py?hl=en&answer=74536 - depends how much you think you would gain from doing that or what sort of non-payment abuse it opens you up to.

I see.

Well, I certainly used to put a few keywords in titles using commas assuming it acted as a separator, however (and again anecdotally) I now write (as does everybody I'm comparing myself to) titles in the format "Cheap Books and Free Books".

Stick 'poker' into Google and look at everybody's titles. A few years back that would have looked like 'Poker, Online Poker, Texas Holdem | PokerSite" where as now it's "Poker and Online Poker including Texas Holdem at PokerSite".

However, stick 'travel' into Google and you'll see everybody still using commas.

So, as I say, I can't think how it would adversely effect you but I think with Google trying to extract meaning from people's searches that, in the long term, more natural sentences over a list of keywords would serve you better.

Hmm, I've not tested conclusively but I can't think how a comma would adversely effect you. However, anecdotally, I've seen lots of sites move away from commas and pipes in titles so I'd have to assume that something was up.

I don't think stop words are being treated the same as the used to be with Google trying to figure out intent more and more, plus I'm not a huge fan of special characters (not that a comma is that special) in the title so unless it looked ridiculous I'd consider not using it.

A few things to think about.

If done right I don't think this will effect your rankings much, if at all. You're certainly not the only site that does this and although I've never done something similar with a php header redirect, georouting of visitors based on IP is something I do all the time (and could be something you might want to look into? - http://www.maxmind.com/)

Your concerns here should be how is Google getting around your site? Is your homepage just a location select screen which it then has to crawl individually (a la paradisepoker[dot]com) or is there a default site they'll see and only later find a link to the location versions? If I (or specifically Google) don't accept cookies what can I see?

People linking into your site will be splitting the value a bit, even if you use the canonical tag. What version of the site do you get links to and is that ranking better than the location variations? Would you be better not using the canonical tag but targeting links into each with location qualifiers to keywords?

As I say, if it's done right I don't think you'll be hurting yourself, but would need to look into it a bit more to say for definite.