I've got it in several places on my bike. I'm also the goofy bastard that used it in the head.
I had grooves in the camshaft bearing surfaces, I used it to smooth out the surfaces. I got 1000 miles on it, but the combination of friction and oil pretty much wiped it out. I'd say it had more to do with the friction part. Use it to patch holes, repair threads (fill, drill and tap, or smooth out dents and dings, but I wouldn't recommend it for any friction points. Leave that for professional welding rods.
It does handle heat well, but does not conduct electricity so don't use it to repair any electrical connections. Found that out the hard way on a ground connection..
as my wife says, should have read the directions!!