Gdatafs is a FUSE implemtation that mount picassa web and youtube to your filesystem. An experimental implmentation of google docs is also avaiable in trunk.
Picassa web
The filesystem support full read/write and delete of album and photos.
Youtube
Supports playing and copying of youtube files (will copy hd content if available, otherwise mp4). Default directories with standard feeds, most popular etc. Your own favorites, and a search folder where you can make directories for search.
Google docs
Supports reading of files.