Watch out for fan noise ...
I have a "bone pile" of external drive cases ... lots of "whisper quiet" cases that were really raging hurricanes of sound. If you plan on using the eternal drives a lot, you will probably need some form of extra cooling beyond passive radiation. (In that case, life is a crap shoot ... I have yet to find a drive case with a fan that is as quiet as the mini.) If you don't, then I highly recommend finding aluminum drive cases that work off of passive cooling.
My most recent experience was with the "miniStack v3". I have a 750GB media drive that holds all my movies and music. My mini serves as the streaming media source for an Apple TV in the living room. With the 750GB drive, the fan came on withing seconds of the drive spinning up. It was very loud. As an experiment, I put in an 80GB drive that runs much cooler. It does not spin the fan up, but that drive is loud and the aluminum heat sink that attaches to the bottom of the drive seems to act as an acoustic amplifier.
I ended up putting the 750GB drive into a vantec nexstar-3 USB/eSata case for the moment. (Purchased from NewEgg.) Based on my benchmarking, the USB maxes at ~19MBs, using the FW on the ministack3, I was getting ~41MBs. So, I will be looking for an equivalent FW case to the vantec one. (I would love to see eSata on the next hardware turn of the mini, but I will take FW800 offered!)
One further observation, for my external drive, the drive will spin down when not in use ... thus keeping things cool. The Mac OS seems to "poke" the drive at regular intervals. I hear the drive spin up, then after a while spin down. I am hoping that this spin up/spin down cycle does not shorten the life of the drive. I wish there were a way to control the frequency.
