Ah, I use to work at an authorized Sony repair depot, and I can tell you this. The YLOD is an all-encompassing problem, meaning there could be many things wrong with your unit. But the problem is located with the motherboard. The older model motherboards are pretty prone to failure. IF you do take it to get repair, they WILL WIPE OUT YOUR DATA. They will give you the same unit back complete with backwards compatibility, but as of right now, there is no way to fix a YLOD without them wiping your hard drive, and reinstalling the OS. They were charging $179 (+shipping) CND at the place I was working at.
Also don't think that you can just take out your hard drive, and sent your unit in without it. They will still fix it properly and everything, but when you get it back, and put your hard drive back in; It will prompt you to reformat it. (And therefore lose you data) There is no way of getting around that. So, basically, all your files are done for the minute your saw that blinking red light. Sry.