It is basically a cheapo Network Attached Storage device. From the reviews I've read the big downside to the Ximeta product is that it requires special drivers to be installed on each machine that accesses it through the network. Also, it can only be written to by one user at a time. It really doesn;t have the full functionality of a real NAS device (which of course costs several times as much). All in all, you'd be better off grabbing an external USB hard drive (which seem to be going on sale on a weekly basis nowadays cheaper than you can build one yourself out of a drive and an enclosure) and sharing it across your network with your other computers.
The NetDisk is a cool idea, but the implementation is a bit flawed in the first generation. A later version may eventually offer beefier NAS-like functionality, and the product may one day really take off once you get it to the point it practically has plug and play capability with your network. I could see a use in the home for this kind of product, once they get rid of the rough edges, like the proprietary drivers.