Having the same problem, right out of the box. Very unhappy. Another post says the new update fixed it, but that's not accurate. Just updated, replaced battery, changed timeout options... tried everything. After update the problem is now worse. If I can't get them to straighten it out by Monday I'm returning the phone.
I had the same issue, where the screen would not turn back on at the end of the call, about 20% of the time.
It did not seem to be related to the screen timeout. My timeout was 1 min, but I made 3-5 min calls and it would still turn back on automatically when I went to hang up.
The 2.0.1 update seems to have helped... I have not made a ton of calls, but my screen has turned back on after every call since the update.
It sounds like there may be some bad proximity sensors out there... so if you keep having problems, take it back!
Thank the lord, the 2.0.1 appears to have fixed the problem. It's been almost 48 hours since I got the update and the problem hasn't happened once! Hopefully it doesn't start happening again right as I begin celebrating...
Assuming the problem doesn't return, I can scratch my one Droid complaint. I really love this phone...