Is your MacBook shutting down by itself? A German dude came up with a solution to this problem, caused by a heat sensor cable that's too close to the heatsink on the CPU. That heatsink expands when the MacBook gets hot, to the point where it actually touches and melts the insulation on the heat sensor cable, shorting it out and turning off the computer.
The solution? Crack open the case and put some insulating tape around the cable where it gets close to the CPU heatsink. Sounds like an easy fix, but it's also something design engineers could have noticed, too. WTF, Apple?
Solution for Sudden MacBook Shutdowns [CrunchGear]