To me, the drobo seems like the "idiot proof" solution. When I was looking for a raid storage solution, I was first drawn to the drobo for obvious reasons (ease of use, looks, campatibility) but decided eventually it was not for me. I've heard things about them being slow and not all that great so I began to look around more. IIRC the drobo is like $500, for a little over $300 I could have bought a 4 bay raid enclosure from OWC that had not only fw800 but esata, usb, and fw400. I would lose functionality this way because I would have to buy all the drives at the same time and set the raid up like that. The I discovered the QNAP NAS. This gave me all* the functionality of a drobo (which mainly includes RAID level migration and expansion) along with so much more. The model I picked, TS-410, was only $450. So it was cheaper than a drobo and is basically the same footprint but with added functionality. So there are other options out there. I'm not saying the drobo isnt good, I just don't think the device warrants its high price tag.
*The only benefit to the drobo over any other solution was the mix-n-match of drives with different capacities. This didnt really matter to me since I wanted to fit it with 4 2tb drives anyway