For those of you who want to take screenshots of the Galaxy Tab, perhaps for posting the screenshot on your blog, Joe from MWD shows us how to do it:
All you got to do is hold the back button and hit the power button (twice, in most cases) and it will say on the screen that the screenshot has been taken and that the image was saved. You should be able to see the picture(s) under your Gallery App with folder name called Screenshots. Or just open File browser app and scroll all the way down until you hit the folder name Screenshots.
Example screenshot from a Galaxy Tab: