Here are the bugs I encountered with iOS 8 beta 3 on my 5s:
1. Facebook worked fine at first, eventually pictures/videos stopped loading.
2. App store app broken. Have to let the app fully load before you can use Search, and even then search was broken.
3. Headphone controls stopped working on any music/podcast apps (Music, Downcast, Amazon Music, etc).
4. Horrible battery life. At 5PM, I was down to 20% whereas with iOS 7 I'd still be at 60-70%.
5. Occasional spontaneous reboots.
6. Never got wifi calling to turn on, probably because I'm on a prepaid account (not really a bug, I guess, probably a t-mobile limitation).
Went ahead and switched back to iOS 7 for now. iOS 8 is kinda "meh" until it's released and we get keyboards, extensions, widgets, etc.