I did this setup with an LED strip, MOSFETs, and a separate 12V power supply: http://forums.adafruit.com/viewtopic.php?f=8&t=69691&p=353076
See 5 posts down of a picture.
This setup has apparently fried 2 of my Beaglebones.
I tested the gate pins on the MOSFETs (which were the only thing connected to the Bone) and they were only reading about 200mA.
The Adafruit customer support says they don’t think this would be capable of frying the board.
I’ve been searching trying to see if somehow this tripped a fuse or something on the Bone.
One of my Bones the power light comes on, but it won’t boot (Rev B). On the other (Rev C), the power light flickers and then goes off and nothing happens.