I've seen Jellybean. My sister is on Sprint and her update finally dropped down last night. It wasn't a large download and it took about five minutes to do. But what I observed:
* The lock screen acts a little differently
* Google search bar takes you to Google Now and it will ask if you want your calendars, etc. synced with it.
* The status screen is a bit different, a little larger font, the settings button was at the very top
* Folders on the screen were different (kind of like how Ice Cream Sandwich looks when it isn't skinned by others) They were almost circle-like
* The easter egg was cute (to activate Easter Egg in almost any android phone, go to Settings-About Device. Tap rapidly on the part where it says Android Version until the screen changes. Our Easter egg is flying ice cream sandwiches this one is a giant jellybean. If you hold your finger on it it explodes into many jelly beans and you can move them around with your finger)
That was what I observed with the few minutes I got to look at the phone. Maybe the hold up is skinning. I must admit when I got this phone I was disappointed that it insisted on making folders look like boring folders and not circles like unmolested ICS has.
She's running Android 4.1.1.
Nothing looked that earth-shattering or life-altering to me. 