The iFolder project just came to my attention.

http://www.ifolder.com/index.php/Home

iFolder runs as an application on Linux, MacOSX, and Windows. It hooks into the OS of the platform it’s running on and then provides synchronization with a server running the iFolder server. Similar to the .Mac iDisk, you can drag files into the iFolder directory/folder on your desktop and then iFolder will sync it with the server automatically when the computer is connected to the net. Files are also available via a web browser as well as the local filesystem, so you can access files stored in iFolder on any computer you happen to use. This has implications for filesharing and automatic backups. I haven’t tried this yet, but plan to in the next week or so. I’ll update this post when I do.