Although this is in murky waters with the GMail terms of use, it is possible to use GMail as a filesystem (the filesystem sends mail containing the file in question to GMail to store), and GMailFs is one such implementation of this. Also there is an extension for Firefox called "GSpace" that does the same thing.

http://fuse.sourceforge.net/wiki/index.php/FileSystems

Gmailfs http://richard.jones.name/google-hacks/gmail-filesystem/gmail-filesystem.html

GSpace https://addons.mozilla.org/en-US/firefox/addon/1593

Mount a Gmail Account as a FUSE Filesystem http://wiki.vpslink.com/index.php?title=Mount_a_Gmail_Account_as_a_FUSE_Filesystem