I should have known better. When I first got my 20 gb PS3, it was clear the hard drive needed to be bigger. I could barely save two or three games on it. So I had a 250 gb hard drive installed. Before the installation, I saved all my data to a flash drive. If I didn't, I would lose everything.
Fast forward to Christmas Eve 2010. My family is watching a Venture Bros DVD on the PS3. All of a sudden it shuts itself off. The PS3 never did that before, so I try to turn it back on. It won't. That's when I see the YLOD first hand. My console is 4 years old, so the warranty is expired. I never continued to back up my data. Stupid, I know. I remember the moment when I hit me. Since I went through replacing the hard drive already, I remembered the PS3 re-formats every new hard drive that's installed. Duh. Well, all is not lost yet. There are ways to try to save single player data after the YLOD. The best way, I think, is to send your PS3 to a professional third party repair shop. Not only will they repair your PS3 and give you it back. (Which Sony doesn't do) Some places will also try to fix the PS3 just enough to recover data. So even if the fix isn't permanent, at least you will have your data.
Hopefully, the PS3 will start offering cloud saving to Plus subscribers with the new firmware update. I'm not a Plus member, but I will be if I can save my data online.
For complete details on what happens after the YLOD, what data will be saved and lost, and what you can do click here