I just returned from an 8 nighter at BCV, and we took full advantage of SAB. Despite the fact that some people complain about the "long" walk from the villas to SAB, it really wasn't that bad. The temps were in the 70's all but one day, and so we were in quite a bit.
It didn't seem to be too crowded until we got later in the week and into the weekend, then it picked up a bit. Talked to one CM there and I don't know how accurate this is, but he told us that before they started the wrist band program at SAB, they took a count of people who were at SAB and not staying at YC/BC/BCV. They estimated around 2,000 for the week.
They were checking wrist bands, but there are several areas around SAB where you could easily walk in without encountering a CM. Saw several folks without wrist bands on. I would speculate that if the pool started filling up, those people would have been asked to leave.
Brian