I am still considering using the crashplan client to backup to/from a friend's house, so that we each have a local copy of the other's most relevant data. This brings me back on topic, as I am too considering getting a Drobo just for that. Because I have a server at home, I don't need the FS version, but rather the S version to connect via eSATA to the server.
Alternatively, I see Drobo has announced a 5D version (USB3+Thunderbolt), which on paper should perform even better if you have one fo the two interfaces available.

One more thing about the Drobo that you may find useful: it is not as quiet as the Synology I've used. Because I only used those in a office with various PC and equipment, I can't tell how noisy it would sound at home. Since I could tell the difference between the Drobo and the Synology (the latter being virtually inaudible), I tend to be a bit careful in recommending the Drobo in those cases where you keep it on your desk very close to you, though.