We'll, I've been using ios 7. I've found a few apps that either don't work at all (such as Wikipanion) or rarely work (apple's podcasting app), but most apps I have found do work, and I've found good substitutes for those that don't (such as
iCatcher for podcasts).
The downside is that the phone reboots far more than it should, but it's far more stable than iOS 6 was at this stage, and also less power hungry (although I'm hoping that will improve, as power efficiency usually improves somewhat as the betas progress).
Personally, I feel that iOS 6 looks old fashioned now, and if I went back, I'd miss the increasingly Google Now like notification centre and the quick access control panel that you can use to control the volume, Wifi, Bluetoth, Airplane mode and a couple of other things from any app.