Since I worked at Rockwell Collins in 2002-2003, deploying over 1000 XP machines while running out of server space means "why can't we use the computer for space?" I've watched a number of filesystems show up that try to do this in some fashion: most of them for clusters and SANs. Let's be honest: my skillset right now is hardware, semi-competent networking, and an ability to program; I'm not putting together million-dollar clusters.
More or less, what I want to do is: use space on machines I administer to provide storage space; enable some kind of redundancy should one or more machine be off; have this space work in a P2P fashion so I don't have a master to worry about; and be able to use it from Windows or Linux clients.
Stuff I found to get started
Writing a FUSE-type filesystem with Ruby
Available file-storing databases
http://www.sqlite.org/ (could save files as BLOB data)
Peer-to-Peer with Ruby