Personally, I'm in the minority of overclocker that think burn in is complete crap.
It's not like breaking in an engine. It's the total oppostite. Overclocking will cause errosion of the traces inside the CPU, the faster you run it, the faster it will erode. I believe that it will not give you gains on your clockspeed. If you can hit a certain speed to perform your burn in, you should be able to hit that speed anyways without it. Upping the voltage for a burn in, in my opinion doesn't accomplish anything but heating up the CPU, and we already know that CPUs run better cold.
Some people swear by it. But not me.