I've been to this the last two years, and it was an incredible time both times I was there. From the looks of it, this year is going to blow the last two out of the water.
The Grateful Dead
The Black Crowes
String Cheese Incident
Peter Rowan Bluegrass Band w/Tony Rice
Plus 20+ other bands and electronic music into the wee hours of the night.
4 days of camping, an alternative energy seminar...hell...there's even a circus in town that weekend that's right by the venue.
250 bucks, July 2nd-5th 2009. If you're in the area, or even if you're not, I highly recommend this. Should be an excellent time.