Has anyone come across any 3rd party PSDrive providers? It would be interesting to see something for other filesystems, such as ext3, ufs, and so on.

Now if someone would come up with a ram drive provider that would be cool, IMHO. 

You could use it as a workaround in those cases were you end up having to write stuff to disk and then turn around a read it back in, and the I/O gets to be an anchor.   Export/Import csv and clixml come to mind, along with using data from command line utilities that only know to write to disk.