Inspired by a USB beverage warmer made from the Pentium processor, I've decided to have a go at making my own:
+5V usb input going to 3 way switch (off, warm, cool)
Warm circuit: LED to indicate warming -> 2 1-2 ohm resistors in series -> temperature switch to break circuit if temp gets above some value (with defeat switch in parallel with that) -> USB GND.
Cool circuit: LED -> peltier junction -> small fan (to cool the flipside of the peltier junction) ->another temperature switch with defeat switch in parallel -> USB GND
Then of course I make good use of the USB data lines by putting a USB port in this thing.
Any input/you see glaringly obvious omissions that could fry something?

The tough part is going to be finding a Peltier unit. The second I saw the title of the topic, I knew you were gonna go with a Peltier.

Just remember that the USB is only supposed to deliver 100mA initially, and a max of 500mA (must be "negotiated" for), so even if you can power your creation, don't expect the USB port you have on it to be good for any non-powered device

hehe, this was in popsci a few years back.

Hey, I can get a peltier unit from the local science and surplus store