I like the setup of the DROBO, but only thing I don't like is the price tag. $500 is alot for a box that only has the "features" it has and comes with no drives whatsoever. The fact that I would have to buy drives at the same time as the DROBO is what has turned me off from it.
They also have another device now called DroboShare which will allow you to connect it to your network, but even that add-on device is another $200. Nice product, but just too pricey in my opinion.
I am currently using a WD MB Pro with 2 TB. Works great for me, and its plugged in via Firewire 800.