Here's a true useless fact from radiation biology: The dose of total-body radiation it takes to kill a person (so called LD50, a dose which is lethal to 50% of the people who receive it) is only enough to heat a cup of coffee by about 1°C. It's an interesting testament to the fact that it's the WAY radiation does damage, not AMOUNT of energy, that is dangerous.

You can figure it out for yourself if you're so inclined: This dose is 4 Gy = 4 J/kg. All you need is the weight of an average person (~70 kg), the heat capacity of water (4184 J/kg), and an estimate of the volume of a cup of water (0.25 kg). Presto!

Edit: Ok, I calculated it. It's more like 0.27°C (0.46°F).