Before you do, please consider visiting one or all of these excellent links:
An open letter to Mr. Stiller by Dave Hingsburger.
Just the facts on Tropic Thunder by Patricia E. Bauer.
Bravo Dreamworks! What courage it must have taken to make fun of retards! by Steve Gorelick.
And please consider mentioning these sites and their take on the issues (mis)handled by this movie to others you know who may be considering spending their money on this movie.