Use your Gmail as an external drive

GMail Drive is a Shell Namespace Extension that creates a virtual filesystem around your Google GMail account, allowing you to use GMail as a storage medium that enables you to save and retrieve files directly from inside Windows Explorer. It literally adds a new drive to your computer under the My Computer folder, where you can create new folders, copy and drag'n'drop files to.

For PC only: GMail Drive

There is a software for the mac users as well.

For Mac only: gDisk