I was glad to find this bluegrass thread, because I'm what they call "bit bad" by the music. I play several instruments well enough to enjoy myself, but not "professional" caliber. That's what's great about bluegrass: beginners can join in and make music with hot pickers who could start fires. It's really music for all levels of ability, and all ages.
We went to several festivals last summer in the Northeast, and my source is the magazine "Bluegrass Unlimited's" annual festival listing around January, Cuzin' Isaac's Guide (P.O. Box 252, Alstead, NH 03602, usually costs about $5) and picking up flyers at each festival. But proceed with caution. These festivals are totally addicting!
Also, take a look at the newsgroup bit.listserv.bgrass-l for discussion, festival.com for listings of all genres, and search something like yahoo.com for "bluegrass."