I used to put them in the microwave for about 10-15 seconds.....it warmed them just slightly, softened them, and I felt like I was eating a warm brownie fresh from the oven!!.
They are also groovy chopped up and mixed with a pudding (1/2 a bar + 1/2 a pudding = 1 meal)...
A tip if you put your bar in the microwave... learn from my mistake... Make sure to take it out of it's metal packaging... Or the micro will make popping/exploding-like noises and the bar will taste burnt and not edible!.
Carry it around in your pocket for a little while before you eat it softens it up by doesn't get mushy.