>I've never attended those in the past -- do they usually take place in an area with a piano, or is it strictly bring-your-own-instrument?

Doug,

There's usually a PA/mixer, mics, a couple of amps (guitar/bass), and a drum kit. As for the piano/keyboards I do recall seeing them in the past but I don't recall if they were part of the equipment rental or if someone brought one down.

Laterness,
Jon