When the nook went from 2.1 to 2.2 there wasn't a noticeable difference in responsiveness. So my guess is it was a big benchmark win but not a big usability win unless you were trying to do number crunching on a tablet.
I had noticeably less UI stutter and freezes going from 2.1 to 2.2 on my Nexus One. 2.3 made it a new phone - the low pause GC really makes a difference for UI responsiveness.
