I've been running nightlies for maybe 8 months to a year now. I update every few days to a week. I've had two issues in that time:
1. When the alarm clock app was rewritten/significantly changed it began crashing in startup. Cleared the app data for it and it worked fine.
2. More recently, when they merged in the 4.3 branch from AOSP, it required an update to gapps as well. I didn't actually read the change/upgrade logs and ended up just reinstalling my phone clean.
Really not all that many problems when you consider it, and not all that serious. The worst case scenario (reinstall phone, restore from backups) only came up once.
1. When the alarm clock app was rewritten/significantly changed it began crashing in startup. Cleared the app data for it and it worked fine. 2. More recently, when they merged in the 4.3 branch from AOSP, it required an update to gapps as well. I didn't actually read the change/upgrade logs and ended up just reinstalling my phone clean.
Really not all that many problems when you consider it, and not all that serious. The worst case scenario (reinstall phone, restore from backups) only came up once.