] GmailFS provides a mountable Linux filesystem which uses
] your Gmail account as its storage medium. GmailFS is a
] Python application and uses the FUSE userland filesystem
] infrastructure to help provide the filesystem, and
] libgmail to communicate with Gmail.

This is a fucking brilliant idea! If I was giving out an award for hack of the year this would be in the running. Yes, python is a brain crushingly inefficient way to implement a filesystem, but Gmail is still likely to be the bottleneck. Google probably won't like this because they don't really expect people to use all of the space they have, but they probably can't stop you from doing this either. Got to port this to OSX!

GmailFS - Gmail Filesystem (dot mac for linux for free)