I have iOS7 installed on my work iPhone. Its a developer release. My initial impressions were -
1. Its too bright (white) - I immediately wished that it had a "dark" theme
2. Color palette would take some getting used to.
3. Settings remain unchanged (sigh) but thats not too bad I guess
4. Loved the BB ripped swipe to go back.
5. Love all the new features - it was about time they showed up
As its a developer release, notification center crashes now and then. Overall quite stable. Its a major UI overhaul and would take some getting used to. Its nice to see Apple push risky changes out in the open. I want to see how popular iOS apps react to these changes. Its going to be all good going forward.