I wonder why noone has ever though about forking iFolder, remove its ".Net"/Mono dependencies and integrate it into Gnome. If you add some P2P and Crypto working capabilities to share big files with friends it would be great. The idea is simple, the original code is tested and opensourced, however it has never gained enough traction to work. I wonder why.
Personally, I had the chance to test it some years ago and it totally felt like a "private dropbox", however the server side it is totally linked to Novell products and installing it in Ubuntu/Debian/RedHat/CentOS is more than painful (if not almost impossible).
OTOH, when what you want is a dropbox replacement, you want it to work seamlessly and automatically
My 2 cents.