There's not a lot of functional changes that i've noticed so far. The main one being that the Battery Use app doesn't just tell you which processes used how much power, it also has graph showing how much battery you have left over time, with a couple lines underneath showing when the screen is on, when the GPS and WiFi are in use, and when it's "Awake" (not sure what the difference between that and the screen being on is.) Aside from just looking cool it can occasionally help you diagnose battery problems. In particular it helped me figure out the one bug with this version that i've encountered so far. The battery was draining really fast right after update and it turned out the WiFi wasn't turning off when i turned the phone "off." Turning off the WiFi manually except for when i'm at home and want to use it has fixed most of the battery drain for me. It seems like i'm not the only one having the problem, though according to some claims at least just turning off the WiFi hasn't fixed it for everyone.
Most of the other changes are just cosmetic. The phone and browser icons are green now. The Task bar has changed a lot, it's got a black background and it's a bit smaller, or at least all the icons look a lot smaller. They're also grey and/or green now. I don't really like the look of the new taskbar that much, especially not the little tiny icons, but i've seen reasonable arguments that it makes it easier to watch video and such with black backgrounds without having a high contrast white taskbar along the top of the screen. Personally that never bothered me, but i guess the change helps some people. And finally when you turn the phone "off" now instead of just having the screen go black it does that old style TV thing where the screen shrinks down to a white horizontal line which then collapses to a point. Kinda a cool effect, but also a little strange.
Anyone else with Gingerbread (i know there's at least a couple of you ;) know of anything else cool and new that i should keep an eye out for?