BlacX to Drobo is a natural evolution to me, as eventually you have piles of random drives with the same stuff on them; why not take advantage of them at the same time?
I haven't looked into this drive for a long while, so memory is fuzzy, but I believe WD also came out with a server-grade Velociraptor that doesn't have the heatsink edges. I can only assume it was the proper 2.5" length, but I truthfully don't really remember.