They still get going a little faster than they know what to do with so they end up falling off. They currently go in spurts. Meeka will sometimes start running with her front paws on it not knowing how to get her back end up once she gets started (she's pregnant, so a little clumsy). I'm thrilled they like it!
If anyone is interested in making one my dad did a great write-up on how he made it. He is going to submit it to a woodworking magazine in case they might find it amusing and different. PM me if you are interested.