There are many types of recorders. The most common ones are DAT (digital audio tape) recorders, mini-CD-recorders and standard analog tape recorders. Usually the person will sneak them in their pants or handbags, along with their microphone. I personally use a single handheld, but I know other tapers who stealth with small tiny mics you can clip onto your hat that have a right and left channel. My mic has 2 channels but its on one piece.
I personally have made a specific hat for such stealth recordings. If I sucessfully get my gear in, I go to the ladies room and "suit up" get the tape gear and mic/hat in place, then go take my seat. Its a funny looking baseball cap though, like from the 70's with a Montana fish & game patch on it (and Im in California, lol). But it works.
I use a Sony D-8 DAT, with a Sony handheld microphone. However, when I can "patch in" to someone who has nicer, more expensive and very hi-quality mics I will do just that. In fact I was at some shows this weekend when all I did was patch in.
All's I can say about "bootleg taping" is IT SHOULD REMAIN FREE. NEVER, EVER SHOULD SOMEONE SELL IT FOR PROFIT ON EBAY! I never have done so, although I could have. It brings me enough happiness seeing the tapes I make spread around and bringing smiles to faces!
PS - word to the wise ~ if your going to BUY ANYTHING, do RESEARCH beforehand. There are many tapers forums on the www, do your homework before you buy equipment cause its not all the same!