actually, fw400-800 cables do exist. Anyway, why do you NEED firewire? Remember, just because something is connected with FW800 doesn't guarantee you 800Mb/s. I've read reports that the Drobo averages around 15MB/s write where as my NAS over Gig Ethernet writes at about 28MB/s on average. That was the point I was trying to make. If you have some other specific reason why you "need" firewire, then by all means disregard my post.
Yeah, I think that for 90% of all people USB 2.0 will work fine on Drobo. All we do is put our bittorrent movies *COUGH* i mean store bought DVD's on it and they all stream fine in 720p.