I used to accidentally hit that button a lot, but I've adjusted somehow and it rarely happens now.
One thing I will say about the Evo -- if I accidentally press something, it opens quickly and I can get out of it just as fast. With WinMo, if something started accidentally, it would take a few seconds just to open, and then I'd have to go to the task manager menu to kill it. So I'd lose like 5-10 seconds if something opened by mistake (the camera was a special case -- that made me lose 20-30 seconds). On the Evo, I can pretty much hit the back button and close the errant app immediately. So now it's down to a couple of seconds.