Major issues with iOS 7 on my iPad 3 (Wifi + GSM, 64Gb).
The App Store app has trouble connecting to the app store. It's not a network issue, as I'm able to reach the app store and itunes from other devices without any problems. Searching the App Store for an app takes 10-30 minutes because of the more-often-than-not "Unable to Connect" issues. And then to cap it all, the App Store app can lock up completely.
The battery drain is far greater than iOS 6.1.3.
Probably related to the battery issue: Other data usage grows continually at a rate of 0.1Mb every 2 minutes, with airplane mode on, locations services disabled, with no apps installed, immediately after a fresh firmware restore. It doesn't matter if the iPad is in use or on standby - the increase in Other data continues regardless. iOS 7.0 with no apps installed uses (747Mb) almost as much "other" space as iOS 6.1.3 used with over 450 apps and a number of photo journals (920Mb) before the first swipe to unlock occurs, and it just keeps growing thereafter.
The UI is a bit sluggish. It gets a lot better after the iPad is reset (by holding home and power buttons down until the apple logo appears - ignore the swipe to shut down), but it's still not as responsive as it should be. iOS 7 really needs options to disable to the form-over-function UI stuff (transitions, parallax etc) so that users of older iPads, iPhones and iPods don't end up with usability issues.
The white UI isn't a huge issue for me, but would it have been so hard to add an option to change the white UI components black and the text white? Invert mode achieves a similar effect, but also inverts all of the images in the process, which really isn't desirable.
For that matter, why didn't Apple make iOS 7 skinnable? Surely that would have been the best way forward, allowing users more customisation options and potentially giving Apple the option of releasing additions skin packs on the AppStore.
*Taps side of head and makes a circular gesture*