The Atlanta OpenSolaris Users' Group has been around since Late 2005 (about as long as OpenSolaris!). It meets at the Sun offices off of Windward Parkway and Georgia 400. See their website:
http://hub.opensolaris.org/bin/view/User+Group+atl-osug/

They also have a facebook page

BTW, there's now an OpenSolaris group on LinkedIn. There were about 1,100 members last I saw.