I installed it on my iPhone 4GS and I did NOT like the new "default" look. Had to change the background because it was too light and the icons were hard on the eyes to see. Better with darker background, but I'd like to change the icons and folders too but don't know if I can... suggestions any one?

Speed- don't see a difference. But then the 4GS is not a speed demon. Wife is getting a 5C today- I'll let ya know.

Pluses: voice to text is much better.
Siri is supposed to be better but haven't tried.
Haven't checked out all the apps yet... mail, and browser seem the same with "new look". Some apps have also changed appearance when opened (stock App)... too early to say better, same, or worse.

At this point- I'd say it's OK (+s and -s)... time will tell.
David (OFI)