it happened to me, so yes. :-)
Why would someone put a blanket on their PS3 . . .
A PS3 (like any form of electronic hardware) has a certain 'failure rate', meaning some just came out of the factory a bit bodged, so you can't always avoid a YLOD. But the PS3 was designed as a media hub for a the home, so it can easily be left on for a few days without it being negatively affected. Of course you always have to keep it well ventilated and dust free. Dust buildup killed my original 60GB fatty, so I've tried taking better care of my new one (vacuum the fans every once in a while, taken it out of my cabinet with a closing glass front)
To be honest, it's pretty hard to tell if your PS3 is going to konk it until it shows the vital signs: regular lock-ups and freezes, display glitches and suspicious fan noises. If you're PS3 grows these symptoms, back it up and start saving money!