> Unison is much more flexible, and actually made for that purpose.
Yep. Unison supports arbitrary peer-to-peer synchronisation rather than just the client-server model, which is really nice when the server is down, or when the clients are connected by a fast Ethernet that's behind a slow ADSL. Or when you don't want to setup a server in the first place.
The issue with Unison, however, is that it's an interactive tool rather than a daemon -- having your hosts synchronise automatically requires setting up a cron job. Many people prefer the automated setup of the commercial tools