I've heard YLOD is like RROD whereas your processor or graphics card of the PS3 becomes overheated so it destroys the mother board and some other components.
Similar to that concept, except many people believe that the cpu/gpu got a little displaced when overheated. A permanent fix would be to re-ball which pretty much replace those balls under the cpu and use lead soldering. Too bad not a lot of people have access to those kind of machines though.
I rather just get the new Slim PS3 since it has a very small chance of getting YLOD, I had a fat one.