Although I completely agree whole heartedly with the version control crowd, with the very dangerous game you're playing otherwise (accidents are just waiting to happen, backups or not!), I do think BitTorrent Sync is a viable (sane) solution in your scenario, provided you are careful and patient...
I looked into it when I wanted to basically provide a local Windows workstation with a one-way mirror of my game project files, for testing out builds. BitTorrent Sync would have been where I stopped if I didn't insist on one-way at the time. If you are ever in the market for a similar product but on steroids -- many additional features (fine tuning options, for one) -- you might check out Unison. There's a GTK & command line port of it. I'd personally stick w/ BitTorrent Sync, though, until you actually come across a problem it can't handle.