Katherine, many moderate and deluxe resorts have a live entertainment schedule that varies from time to time. The only way I know of to get information about what's going on, though, is to call the hotel directly. Central reservations, disney dining, and disney recreation all do not have the information (at least the last time I tried 1-2 years ago). So you have to call around to all the hotels, and they may only have the information for the coming week, so you'd have to do it right before, or when you're there.
For example, when I was at the CBR in '99, there was a steel-drum band at the pool bar 1 or 2 nights a week. At the POFQ, in '05, there was a saxaphone/flute player with computer accompaniment who was quite good. At CSR in '05 I do not remember live entertainment. The lounge was mostly conventioneers drinking and eating bar food, and talking shop. Things may be different now, though. I've heard that POR has a great piano player that I think I've heard is there quite a few days of the week.
The crowds are small at these events - they're mostly intended for guests of the resort they're at. So, while not a big-club atmosphere, they could be fun.
Without a car, though, it will be tough to go from one resort to another late at night. If you can transfer busses at a nearby park that is open, then it won't be bad at all. But in December the park hours might be too short if you want to stay at the lounges very late. You can always go through DtD, but that can take a LONG time. The best way is to get a cab. That'll cost you between $10 and $20 (incl. tip) depending on which two resorts your going between, but it'll be a LOT faster.
Have fun on your trip no matter what you decide to do!