I am with EE actually so that's comforting. It was not so bad the other day but noticed it today in the train. Lost signal, signal then came back but 3G/data didn't. Rebooted, nothing. Didn't even come back when I was in the house, reboot again and it finally came back. Seems that it's fine until you lose signal, when signal re establishes itself you get cellular (calls/text) but not any data until rebooting, and even then it's sporadic. Not a signal issue and toggling data on off doesn't do squat. Real shame as aside from this every thing is (mostly) peachy. Almost as quick as it was on ios 6 which I can't complain about.
Edit will try network reset. Don't mind losing passwords if it fixes it. Oh and spoke too soon about speeds, it's on a go slow again. Head >>> wall.