The little bugs I have are not earth shattering but still a little surprising for a global flagship product.
My ip5 bugs that bit me gently so far:
1. The phone even with auto-dim off will sometimes dim to near invisible after coming inside from outside. Weird. Feature is OFF, why is it dimming....
2. When coming out of sleep to wake (not power off) I get a fairly long lag before any Internet communication is resumed.
3. I've experienced random occasions when my email will NOT send. I get a failure. Until I reboot. I CAN get web pages, so that's odd.
4. My phone when connected to my car USB will randomly turn off ringer volume to zero. Missed a few work calls due to this.
Anyway, obviously nothing major, but stuff I hope gets fixed soon
Delete all your Settings via the Settings app (/General/Reset/Reset Settings). This fixed my Brightness issues and made it behave the way it is intended in iOS 6.