We had some problems in June '07 at Pop Century. We were there for 10 days and everyday we brought inflatable rings and sit on themand race. We had lots of fun for 7 days with no problems. On the 8th day a lifeguard told us we couldn't use them. we told him we had been using them for 7 days. He told us that they weren't allowed because he couldn't see underneath them. I'm not sure if there's an official policy, but it is something I'm going to check into before we space to pack them if we can't use them.
The rings we used were very small (or else my butt was very big lol)