Guess there's a moral: When feasible, check out an "open mike" session as a spectator first!

Kat: Are you thinking of starting a song circle first, or going right to arranging an open mike session at a bar? Some classes (for stand-up, jazz singing and such) at "open universities" and community centers end by having a public performance night--and often the "classes" are little more than a way for like-minded folks to get together and share, getting their feet wet in "safe" setting; you'd function more as a moderator than a tutor. Another option you might consider, if you don't mind the lead time.

Gargoyle: Interesting suggestion about performing at farmers' markets.