I have used all iOS versions except 4.2GM rev b and I can't see any change in performance. It's as fast and snappy now as when it came out of the box. But now I have multitasking, folders, airplay and AirPrint. My backlighting is working better that's it.
One happy bunny here, some folks must have very highly tuned visual perception to notice changes of a second or two.
maybe I'm getting old or is it because my first computer was a ZX81.

One happy bunny here, some folks must have very highly tuned visual perception to notice changes of a second or two.