Originally Posted by Jester_rm 
Depends on the system, and I would think it's more common for a drive to fail than an enclosure (but anything can happen). Look for one that has user-replaceable drives...then you should be able to replace drives if they fail or put the old drives in a new enclosure if that fails.
So far, I can't say enough good things about the Drobo. It just sits there, quietly ticking away, and no problems so far. I've had mine since last summer.
I don't know how it works as far as storage capacity goes, I have 3x750gb drives in mine, and it is listing 1.36TB of storage space.