It sucks.
It hiccups very often and is definitely not as liquid is previously.
Honestly, I wish I can go back to iOS4.
I attempted to upgrade my 4S on 5.1.1 to 6 yesterday. It only worked halfway and left my iphone bricked. I do have a back up on iCloud, but hand't done it for 6 months, so I did get all my contacts, but lost about 700 pictures that were on photostream.
Anyway, I just did a fresh backup and will try again today, maybe.