Stock ThunderBolt users are just now getting their first taste of Gingerbread, but all the cool kids are already running versions of Android 4.0 Ice Cream Sandwich based off of the Software Development Kit. Verizon's first LTE phone is the latest to get the treatment, courtesy of the fine folks at RootzWiki. Experienced custom ROM users can flash the software in the usual way via a custom recovery - don't forget to do a backup!
SDK ports are usually a stop-gap before the source code for the latest version of Android becomes available, and that seems to be the case here. Major functions like the touchscreen, audio and data aren't working - basically the only thing that the port is good for at the moment is booting up and looking pretty. That isn't a put-down, mind you; this stuff isn't easy, and I commend the developer "jdkoreclipse" for his or her efforts. A similar port on the Nexus S is a lot more complete, probably because of the ease of creating ROMs for a developer device.
HTC has committed to bringing Ice Cream Sandwich to as many devices as possible, and to my mind, that certainly includes the high-powered ThunderBolt. But given HTC and Verizon's pretty dismal upgrade path to Gingerbread, who knows how long it will take. Custom ROM junkies can take solace in the fact that true Ice Cream Sandwich ROMs will probably start popping up only a week or two after the open source code drops later this year.
Galaxy Nexus Hands-on
Ice Cream Sandwich Hands-on