Thought I'd throw in my two cents on the AdWords Keyword Tool stats:
I'm almost certain that the "new tool, logged in" results are the most correct (and very close to reality) - based on data, not just an opinion.
I'm not a domainer, but rather run SEO for a medium-sized business that has been into SEO for /long/ time. We rank very well for a large range of short-tail and medium-tail phrases, and all of our analytics data points to the "new tool, logged in" exact match results being correct.
A great example if our own brand name. It's quite distinct, we operate in a fairly narrow niche, our homepage shows at #1 with sitelinks when you search it (as you'd expect), and there is no AdWords competition at all in the SERPs (yay trademarks!). Essentially, if someone runs an exact search for our brand name there is a /very/ high probability they're going to click-through to our site. I'd say certainly 90%+, and 95%+ wouldn't be a stretch.
The "new tool, logged in" exact searches for our brand shows 3,000/month. The total visits to our website last month from people who exact-searched our brand name on Google was 3,100. Note I made these numbers up, but have kept the ratios the same as reality.
As you can see, the two numbers are almost exactly the same. The fact that our own stats are slighly higher I would put down to an increase in search traffic from this keyword phrase, combined with the AdWords Keyword Tool data being a three-month rolling average whereas our own stats are for the last complete month.
To me, the almost idential searches and visitors numbers combined with the expected 90+% CTR strongly suggests that to the numbers from the Keyword Tool are correct.
Demo here -
http://www.google.com/landing/instant/
amazing stuff isn't it
What are the implications? I guess it means you need to put more emphasis on ranking early in the complete search term.
My guess is that it's going to be a very good thing if you rank well for short-tail phrases, and a bad thing if you rely upon long-tail.
Consider this: say you run a website that is #1 for "cheap widgets" but nowhere to be found for "cheap widgets for blue cars in melbourne".
Previously, you would miss any users searching for the long-tail phrase. Now, when the user gets as far as typing "cheap widgets..." (or perhaps even shorter - e.g. "cheap widg..."), the SERPs will update to show /your/ website at #1. Previously, they would never have seen your website /at all/.
Some proportion of searchers will continue to type "... for blue cars in melbourne" and pass you by, but you'd expect some to notice your #1 result after "cheap widgets...", stop, and click on the result. So, in essence, you'll end up "stealing" some of the long-tail traffic. And, on the flip-side, I can't think of any reason why Instant would be negative for your existing short-tail SERPs unless perhaps it benefits AdWord advertisers greatly in some way.
Maybe time will prove me wrong, but this seems logical... going to be an interesting couple of months regardless.