A while back I went looking for a WebDAV accessible online drive. There weren't many, but I did find one service called Box which gives you a 1GB drive and an unadvertised beta WebDAV interface. It can be accessed through nautilus but has problems at the moment including that you can't move a file into a different directory and you creating a folder has some sort of problem. Uploading and downloading files works though. These bugs may be bugs in nautilus or the gnome-vfs webdav module though because cadaver works fine (albeit slowly).