I think the only problem I have with Drobo is the horrifying warranty options. For a device that has roughly 80% markup, I think it's attrocious that it has a hardware warranty period (1 year) lower than a cheap USB hard drive from just about anyone else (2-3 years). Especially given that once you're out of warranty, a hardware failure ANYWHERE in that device isn't really recoverable from without going out and buying a new Drobo. You can argue that it's unlikely to fail, but I think that, if they really stand behind the longevity of the device, it should really have a longer manufacturer's warranty.
Whatmore, the extended warranty tops out at 3 years. I think for a device like this, which is essentially luxury storage, it should start at 5 and extend to upwards of 10.
Aside from that, it's a pretty solidly-made device. For ease of use alone I think it's well worth its markup (after all, research and software development isn't free), as it's essentially an intelligent RAID system for the masses that's easy to extend storage on (far easier than ZFS, which I'm using at home). However, they can still go fornicate with themselves for a standard warranty like that. Seriously, I think they're the only hardware manufacturer on the planet with that bad a price/warrany ratio.