This looks very interesting, but the it's a bit difficult to figure out what it actually is from the website. My impression is that it's like a more featureful take on Unison ("two-way rsync" iirc) with a central server to facilitate NAT traversal.

I suppose they probably haven't figured out their eventual pricing model, but I'd certainly pay a few bucks a month just for coordinating NAT traversal, papering over dynamic IPs and a web interface to set sync policy. For the most part, when my computers are sync'd peer-to-peer, I really don't need or want a copy of my data in the cloud -- my boxes _are_ the cloud. That means that their typical incremental cost per user would be practically zero.