Yeah, the detail missing from this is it is apparently an upgrade-related error. The guest account should be disabled on all OSs when not in specific use anyway. Crazy ass bug though, Apple should be better than this by now. The faster development pipeline is making them to the same level of large scale blunders that their neighbors to the north are famous for. Is it worth the price?
Hey, remember how Snow Leopard was going to be all about stability?