We visit every Community Hall at the resorts we have stayed at. We once spent (what seemed like) an entire day at the one at Bay Lake Tower. We had been at Epcot in the morning, but there was a torrential downpour which forced us back to the resort. Kids had a lot of fun playing with other kids there - there was a lot to do and movies playing, etc.
Last year, we got to Kidani early and our room wasn't ready. I didn't plan well and we did not have our swim suits with us, so, we spent hours at the Community Hall waiting for our room to be ready. (Which took until about 5:00) Kids played pool, watched movies, played Wii, etc. while hubby and I had an adult beverage or two.
Looking forward to hanging out at Jambo next week. Hope the weather holds out for you!