My opinion, FWIW, is that it has nothing to do with the charging plate. It's related to the problems that a lot of folks are having with some *process* running in the background and hanging the phone. Mine has hung a few times now. Ya, I'm pretty sure I exited all the apps ahead of time and keep most things turned off, but it happened. I don't have a lot of apps, so it has been easy enough to nail down what might have caused it. I'll delete the app and have no further issues. Not very scientific, I know. I'm with another poster, It'll be nice when MS and Nokia get out their updates.
I'm in agreement with another poster that you should be able to rely on today's communication devices as reliable alarms. That functionality has been built in for a longggg time and many people have come to rely on them. Sucks for the OP and others right now that there's a possibility the alarm won't activate because the phone is hung.
The people who are saying you shouldn't be relying on an alarm... What if, like another poster mentioned, you relied on your phone for an important call in the middle of the night. Solution: get a land line? don't think so. Lots of potential issues right now for people that are relying on their 920 to alert them to some incoming bit of needed information (text, voice, alarm, etc).
That's the cost of being an early adopter. We are not only enjoying a newly released phone, but a newly released OS. I've experienced battery drain, locked up phone, etc and have narrowed it down to some app every time. Just need to use some caution for now IMO.