First Impressions of 2.1
Contacts and typing definitely more responsive, not going to say snappier! Note, I did a full reset before installing so that I could do a like-for-like comparison.
Never really had a problem with backup -- but I only have three pages of apps. But, get this, first back up took nearly a minute and a half (longer than usual). Second backup took about 30 seconds (bit longer than usual). Third backup took less than 2 seconds (honestly not exaggerating!). Quickest ever.
Genius only showed up after a couple of syncs (can find it under Playlists>Genius>Select a Track or tapping album art on playing song, middle of the slider).
Others have already mentioned the new green apps indicator in iTunes memory allocation bar; new GPRS, EDGE and 3G symbols.
Calls and data same as before, but not had a chance to test it elsewhere -- always had good reception at home and work.
All in all, this feels rock solid. A few new features for me, and all in all a bit more slick. Liking this update!