USB Mini Fridge.

The maximum current draw allowed on a USB port is 0.5 amp. So this thing can draw a maximum of 2.5 watt (0.5 x 5)

I think your 500watt power supply can take it.

Also, it's a tiny pelletier element, they are also used to cool some processors.

Also, this is a nice gimmick, the perfect Father's day present for the unimaginative.

I also found a coffe-machine that works via USB. Unfortunately, it only keeps the coffee warm, but doesn't make it hot.

I think I want it. I wonder if they make one that fits a bottle. Cuz I like my beer...I mean soda in a bottle.

A powered USB hub doesn't even have to be plugged to your machine - Unless the fridge has thermal feedback (Bing! Your coke's ready!), you don't bother. I have a hub just for localized light sources and chargers already - This'd be fun, too. And that way you can use it independently of your computer - say, on a bedside table? If you don't sleep with your computer. ;^)

Printers, external hardrives, scanners, etc. etc. How is this going to be worse than those. Do you know how much stress it will put on the system?