Beta 2 was a lag fest and crash city to me on my iPod touch, beta 3 has been nothing but smooth and wonderful for me, a few bugs here and there but they are VERY minor. I am hoping with beta 4 Apple fixes the last remainder of the bugs for iPod touch at least, that way I can live without a beta 5, or 6, and wait for GM.
iOS7 is perfect on my 4s to the point I installed it on my daily driver. The only gripe I have is that I can't use Skype. However that's why I have a laptop right