Me too, using the hacked Pogo Plugs:
I see it's now gone up to the outgrageous price of $10! Used to be $8. Interesting backstory: I gather it used to be sold with a paid service that would let you access your media remotely. The service failed though, and people figured out how to load Arch Linux onto the thing. Works spectacularly well as a NAS using the instructions here:
The Linux goes on an SD card, then you simply connect a USB harddrive. I haven't needed to get fancy with RAID or multiple disks, which I gather it does support using USB switches, but I have a feeling not as well as a Drobo. But hey, for $8 (I mean $10! Ugh!), who can complain.
That said, the company recently made it harder to hack these for some reason by making it harder to enable SSH, which is the first step to load Arch Linux. Oh well, but it's still possible using serial console: