Well my 2nd QNap arrived and I am replicating about 600GB onto it. Going at about 10GB/hour. That is without regular file serving turned off. I'm very plesed with Qnap has gone; Nice UI w/lots of turnkey features for the layuser. But they also let you ssh into the box and have your way with it.
I'll have to try out the encrypted drive feature for backups; That way, I can detach those and send them off-site for safe keeping in case of meteor strike.
If you haven't.. I'd heavily recommend against buying Drobo. I'm a computer geek and I thought that Drobo was cool for all the reasons you mentioned. In fact, I was so sold on the idea that I pushed several clients to buy Pro's. I ended up with 8 Pro's at 6 client locations and have had a 50% failure rate in 12 months. 4 dead in 12 months at different locations.
They were all replaced under warranty, but that doesn't help my clients being down for a day or two at a time.
Backup your drobo... you've been warned!
I have a QNAP TS-659 and have since sold 4 more to different clients.. not one has even hiccuped. They are FAST. Much faster than the drobo even in iSCSI setup. I have a iSCSI connection to my QNAP and attach it to my main system for off-system storage. You can run rsync and a huge number of tools on qnap that you just can't do with a drobo.