I only buy drives one at a time these days, so I don't know how useful my observations are.
I disagree with Mark, the current Hitachi models aren't any hotter than anything else. In fact, the 1TB Hitachi in the PC in front of me is cool to the touch, and therefore much cooler than the 250GB Samsung that preceded it.
Having said that, the case does have a 1000rpm cooling fan in front of the drives.
Not that it means anything sensible at all. You should be looking at power consumption, not surface temperature, and certainly not whatever the drive reports (when comparing different brands). In theory, a drive that feels hot to the touch is getting rid of heat more effectively.
In terms of power consumption, the Hitachi is comparable to the Samsung. It draws less power when spinning up (and possibly at idle?) but more when seeking - because it has slightly faster seeks.
A big thing for me is that the Hitachi is fairly quiet, unlike some user reports of newer Samsung 1TB drives.
