I put off buying a DROBO for a couple of years. The idea of a single storage device that could hold ALL my photographs since I began to shoot digitally was very appealing. I had grown a data farm over the years with multiple external drives from multiple vendors. The stacks of drives along with all the USB cables and power cords was really becoming a pain. Amazon and DataRobotics was running a special - $340 for the Drobo (I have the base model second generation mofel with four drives with the firewire 800) from Amazon and then subtract a $40 rebate from DR. I bought for 1.5TB drives from Amazon for about $109 each. The total cost was about $740 for a single RAID storage device that netted me about 4.0 terabytes vs. seven drives that had no hardware backup.
My main computer is an Apple Mac Pro which has four drive bays and I use them all. So the DROBO is used purely for backup, not day to day work.
Overall the Drobo works as advertised. I put the four drives into the Drobo in about 10 minutes, installed the software on my Mac Pro and it was ready to go. It looks like any other hard drive on my computer, but it is a huge 4.8 terabyte drive. I started moving all my files from those individual storage drives to my Drobo. That took about 24 hours ... not quite as fast as I thought it would be, but you only have to do it once.
One small problem that I have had is that when I put my Mac Pro to sleep the Drobo also goes to sleep (that is good), but when I wake up my Mac Pro the Drobo wakes up but the Drobo Dashboard application that comes with the Drobo can't find it. The Drobo drive is still recognized by Snow Leopard and I can see it in the File Manager, but the Dashboard application can't seem to find it. This is very strange, especially since the operating system finds it. The only way to remedy the situation is to unplug the power cord (the Drobo doesn't have an off/on switch) and plug it back in. Sort of clunky. I have researched all the Drobo support pages and this seems to be the only work around.
The other annoying thing about the Drobo is that when I do almost any file operation, like saving a file, the operating system seems to wake up the Drobo even if I don't select it. When this happens, Drobo spins up the four drives in sequential order and I can be sitting there for about 20 seconds waiting for the Drobo drives to spin up. Since the Drobo is a backup device, I just take it offline by putting it in standby mode. When I need to use the Drobo I have to unplug and plug the power cord.
At the end of the day having all my files on one large RAID storage device that does not require any management by me is a dream. BTW I have two more copies of my files on other drives. I take my production drives when they are full and ship them offsite. If you are going to use the Drobo for production work, you really need two Drobos in case one of the Drobos fails.