One pet peeve I have with smartphones is that lag can greatly affect their behavior. Responsiveness of the screen when finishing a phone call, which can sometimes seem to take forever on my rooted HTC EVO, is an example of this. Fortunately, it turns out that in the settings for CyanogenMod 7 (and possibly other AOSP ROMs), there is the ability to end phone calls by pressing the power button rather than the end button on the screen.
Just go to Settings -> Accessibility and tap the option you see in the screenshot to let you press the power button to end calls.
I think this is a great little tip that should hopefully help out many people who might have tried to quickly end a call but instead ended up cursing out their phone while the person on the other end listened in on them.[Lifehacker]
Update: There seems to be confusion as to exactly who can use this feature. I am, as some commenters pointed out, on CM7 on my HTC EVO 4G. In seeing this story on Lifehacker, there was no mention of this being on a custom ROM or AOSP only. Usually when a tip like this applies to Android phones, it applies to almost everyone but me. In a great cosmic twist of karma to make me look foolish, it turns out this most likely applies only to me and people who have flashed their phone.
I've edited the post and apologize for the confusion, angst, turmoil, and upset stomach this might have caused.