I'm a gadget nut, and so for me what could be more perfect than a gadget mug! It does what it says, when cold it's dark blue with white writing and when you put hot liquid in it quickly changes to white with red writing. The only downsides to be aware of are...whilst there is hot liquid in the mug you can still see the "cold" writing as the white of the mug isn't quite the same white as that of the cold lettering which was a dissapointment. Also as you drink because body temperature is "cold" to the mug your lip marks and finger marks end up all over the mug as it's cooling down and makes it look messy.
Having said all that, it is a great conversation piece, and after a month the novelty hasn't worn off yet!