Just came across this on 6moons:
http://www.drobo.com/
http://reviews.cnet.com/hard-drives/drobo/4505-3186_7-32470303.html
A little spendy, but a cool idea!
I looked at it a few months back but was turned off by the lack of network capability and also it's reported speed. (Some are saying it's slow!)
I ended up just grabbing a D-Link DNS 323 for a lot less money that works decent.
It looks to me like a cleaverly marketed NAS product. I saw it in the Tiger Direct catalog and thought it was nice, but you can build the same with a mini-itx board and a few hard drives for a little less. Though, sometimes it's nice just to buy the thing, stick the drives in it and go.