The main one seems to be dropping calls and rebooting after about 5 minutes into a call.
I kind of get that on my 3GS, but only if the signal drops, which annoying is right where I sit in the lounge! Only usually happens when I'm chatting to my Mum, short calls are never an issue and certainly not 5 mins into it, more like 55 mins! It's probably a good reminder to stop nattering and get on with stuff

However I think one of the next two upgrades were meant to fix it, but I've not run them yet.