It's cool how it does the multi-user realtime stuff, but if you think about it, that's solving problems that almost every networked application deals with (latency, consistency, etc) but in more subtle ways. I'd say really its strength is just how amazingly simple and easy it is to get something going.

It's been a year since I played with it, but at least at the time the weak side seemed to be integrating with any existing systems you may have, whether front or back or middle or sideways. In those cases the magic doesn't work for you and you've got to figure out how to plumb it. (Again this may have improved in the past year.)