I didn't feel like waiting for the carrier to push the OTA to my phone so I got it with the "Clear Google Services Framework data" trick, and so far it's pretty neat.
UI is just as smooth as it gets, both when dragging around and when launching apps.
It also solves one of my gripes with ICS, which was a sometimes quite noticeable lag on the keyboard when autocorrection was enabled. I installed Swift to fix that but now I'm back with the default keyboard and it's super smooth.
All in all JB is awesome, but there's one issue: Google Now results in Spanish aren't nearly as good as in English. Almost every single question you make gets a plain Google Search answer, which isn't bad but certainly not as good as it's supposed to be