Sony has a portable 802.11b file server available in Japan. In addition to supporting most major file protocols (CIFS/SMB, NFS), it can also act as an ethernet bridge. You can also install any other Linux software you can get your hands on. Joi Ito's got one and claims it has about 9 minutes of battery life. The specs seem very similar to OpenBrick. If you're in Japan you can order one here.

Looks like Sony beat Intel/Roy Want to market with personal portable servers, but I hope Intel hurries up with one that runs for more than 9 minute sans power adapter.