UPDATE: This is no longer a free service. I cancelled my account. It still might be worth it if you want the convenience of syncing folders that you specify (versus special folders to a certain service, you can just pick whatever folders you want with SugarSync).
This great for syncing up files between computers, even between a Mac and a PC. This proved invaluable when I wanted to share files and the person was having trouble with my ftp site for some reason.
