They are fairly accurate, but they are estimations. You will notice that the search volume is rounded off numbers. You will see 8000, but never 8001, 8010, etc. Google would want to give their advertisers fairly accurate numbers so that they can pour their money into ppc for the best keywords. Which keywords have you noticed that seemed too high?
When you compare the various sources you get different numbers. I trust Google as much as any. Since it's free I use it a lot, but I also use wordtracker and keyword elite. I just use the 3 to see what the biggest players with the least competition is and then I optimize my sites and PPC campaigns around those phrases.
great thinking depotgang. I too use wordtracker and will take a look at the keyword elite too. Thanks for the heads up!
You need to count on Google's result as they calculate it on the basis of certain factors that no other tools take into account.
I think they will be fairly close, just keep in mind that for popular niches that numbers will be inflated by webmasters doing searches, research etc