My story is that I used the old LaCie 250GB fanless version until full and then last week knowing the Iomega had a fan bought the 500GB LaCie thinking (like an idiot!) that it too would have no fan. The noise was terrible, incredibly loud and annoying so I tried to swap enclosures with the old fanless LaCie and left it to clone overnight only to find the drive had stopped after a couple of hours probably due to overheating.
Anyway went and got an IcyBox enclosure http://www.textorm.com/images/produit/grand/ICY_BOX_IB_351US_B.jpg and shoved the drive in there and propped it behind the monitor, no noise, it's faster though I don't know why and the whole set-up is tidier. The fanned enclosure I'm giving away to a friend to do back-ups with as it is really unusable.
BTW the drive used in both old and new LaCie Mini Companions was Seagate.
No fan and it looks OK in real life even though I've hidden it behind my monitor. My experience with a Quicksilver G4 put me off fan noise for life.
Any standard 3.5" 133 IDE ATA (not SATA) drive works fine and there are different versions with combinations of USB2, FireWire, SATA ports available apparently.