Yeah I meant to include that link to the website. That's probably the easiest way to find info on the band. There's another site run by the fans (I suppose) at
http://www.umphreaks.com. I haven't really checked that out much though.
If you're not into web surfing (but you made it here somehow), they're a 5 piece with 2 guitars, keyboards, drums, and a percussionist. I think a couple of them handle the vocals on the songs that aren't completely instrumental. I know I heard their ex-drummer do an awesome performance of a Sade song once.
No, I'm not kidding.
One last thing is that if you're into free live music, you can often find their shows on
http://www.archive.org/audio or with the Furthur software (
http://www.furthurnet.org) and download them. Perhaps their taper-friendly status is what made them popular with the jamband crowd.