When we went in Nov/Dec, 2000, it was cold so we didn't go swimming. But there were mostly kids in the pool (I think even though the water may be heated, you still have to get out at some time and it is probably a long walk to the room when you're cold!!!) I had a sweatshirt on and I was really cold; there's kids in the pool.
In Nov/Dec, 2001, it was much warmer (a little cool in the evening) and again, lots of people swimming!
We're going back again the first week in Dec and I do hope its a little cold - kind of adds to the holiday spirit!! Check the 10 day weather forecast right before your trip!! Have fun!!!