tedster - 11:40 pm on Sep 10, 2010 (gmt 0)
Any one data point can always be botched. However, a 50,000 search LOCAL terms sounds pretty dubious to me unless it's [pizza] and the location is New York.
More seriously, for any decision that has a lot riding on it, I always augment Google's data with at least one other source, usually a paid service.
You can also see if anyone is actually bidding for ads on the term and get a feel for it that way. Heck, you could even buy an ad with a low budget cap jand learn a bit in real-world application that way.