All externals are hot. I havent found a cool one to date. Hell, I have a 4gb usb 2.0, 4200rpm drive. It damn near burned me once. I mean not really, but in a nutshell it was hot.
Same with my friends 120gb. Although, my other friends 250 wasnt that bad. Although, it was just kinda on, not running when I touched it.
All in all, unless its smoking no need to worry.