...any over-estimations can be waaaaaaay out because they have to multiply up their numbers to estimate demand.
Also, in general, many searches on which there is commercial pressure are skewed upwards because of webmasters checking their positions twenty times a day, which leads to overestimates on these queries.
WordTracker, which uses non-mainstream sources, is actually less prone to this than say, Overture was, because with Overture the positions were on the search engine providing the data.
Google has the AdWords Preview Tool...
[
adwords.google.com...]
...which undoubtedly helps reduce skewing by advertisers, but I'd bet not completely... maybe not even substantially.
Since the errors on WordTracker do get multiplied up, if you see a great many searches reported for very specific queries, like [
red widgets and widget repair denver], you should probably disregard those.
While Google may reveal Trends, Zeitgeist, Insight etc, I'm sure they take a great many steps to prevent anyone from getting their hands on lists of thousands of terms that could be dropped into a database. Hitwise is in the business of selling data, but I doubt that they'd release a top 50,000 list to anyone. I can only think of a few uses for such a list, and it's not likely any of the data providers would want to encourage those.