I'm considering this as well.
1. The phone won't "lock" anytime I talk on the phone for more than 10 minutes. The only way I can revive it is by powering it down. Generally at some point during the call the proximity sensor will stop working, triggering the screen to stay on.
2. The vibrator has gone from silent to sounding like it's going to rattle apart at any moment.
3. The front camera is full of dust.
4. Last night after a phone call and running through my power down routine, the phone cycled 3 times during the power up.
5. This is a gripe for WP in general: No way to just search phone contacts. I don't want my entire Facebook congregation to pop up whenever I try to call my buddy, girlfriend, whoever. Solved Number 5.
If there isn't an update by Tomorrow to fix the locking issues, this phone is going swapped for an iPhone 5. I can't risk being stuck with a defective phone/software seeing as the 14th day of ownership falls during thanksgiving.