I'm using the Dropbox Sync for playing the same World on three different PCs, one Linux-machine, two Windows7-machines. All machines have their "saves"-Directory linked into the Dropbox. As long as you don't run Minecraft simultaneously on more than one of these machines, it works pretty well :).
The initial sync is a bit slow because of the many files, and you should turn off the Dropbox Tray Notifications (because they become annoying with so many filechanges). I'm willing to write an own guide for this, if someone cannot adapt the "Saved Data Dropbox Guide" to my solution.