Yeah, I've looked at RabbitMQ in the past (and I suspect it's much nicer than Apache's ActiveMQ which is the only AMQP thingum I've used). It has a nice site of friendly client-side libraries, too, for various languages, so it'd probably be what I'd plump for if I went that route.

It only takes care of the messaging part, though; I feel like there should be something out there that builds a layer on top of this and automagically syncs data. Nothing quite seems to fit the bill, though.