Yeah, what Trott said. I have 9 BPs, and I usually take one or two out per day and let them tool around the bookshelf or whatever; they're also sharing tanks, 3 each to a 60 gallon tank.

But I'll have to break down and start using racks pretty soon. This setup is pretty sweet, but it's just not practical for a large number of animals. And I'm very curious to see if there will be behavioral differences between the well-socialized animals and the tub dwellers.