Dale's comments on tuning are interesting. I'm a beginning banjo player and have been for a couple or three years. Compared to guitar, the banjo is a little less stable, but I think the real reason for all the retuning is that banjos are tuned to what on guitar would be called an open tuning (that is, the open strings make a chord if played all together). This means that to play in different keys, the banjo either has to be tuned to a different chord or it has to be capoed, which also results in some minor tuning adjustments needing to be made. So while I tune my banjo, perhaps you can read this viola joke:

A conductor was rehearsing a symphony orchestra when a viola player suddenly screamed, jumped up, and started thrashing the brass player behind her with her bow. The conductor reprimands her severely and asks "what is the reason for this unprofessional conduct?" She says, "This guy reached over and turned one of my tuning pegs!" The conductor says, "Well turn it back and let's get on with the rehearsal." She says, "I would but he won't tell me which one he turned!"