That is an interesting distinction. I am definitely using their storage system as a back up to my own hard drives (which I have no intention of eliminating). What prompted this for me was that I was using several external enclosures to back each other up - something I found dreadfully painful - particularly as space is a premium on my desk. :P
Now, I am keeping the same number of external hard drives - but now as the primary source of data. The Drobo, with its hard drive redundancy system - is the back up of my current hard drive system. Prior to this, I was backing everything up an additional time by burning DVDs - which is a horrible way of doing business.
It is my hope that this will hold me over until I can realistically start uploading files to an off site server.
james, also note that the drobo is not really a backup system at all, it's a storage system that allows you to story your data together and in the event of a drive failure your not going to loose data. you must back up the drobo or you're really only using an expensive system with a lot of capacity to store stuff . . . transfer speeds depend on many things, drive speeds (the good deal drives you put in it may not be such good deals) the speed and type of connection, the operating system youre using, the capacity of your computer and file sizes. If youre moving all that data at once is will transfer at a much slower rate than if you were transferring smaller packets . . . that said, you have to be there to copy and past all the time . . . I think it took me about 10 hrs to load my drobo . . . you saw my set up, win 7 pro, esata, PC with 64 bit quad core, 24 gigs of ram, solid state c drive, and the drobo as the fastest drives made at the time i put them in, about a year ago now . . . I paid a little more for them but i wanted speed . . . as for getting drives cheep you cant get them cheep enough to buy more space than you need . . . drive prices drop in half in a year and size doubles . . . I think it's best to grow the drobo with new drives - today i can add a 3tb drive that's faster than my 2tb for less than i paid for the two TB drives one year ago . . .