In 2010, I had to move to the Eastern Shore of Maryland. In that time, my cousin gave me his old computer for usage and asked to borrow my 360 in return, with the terms being he'd return it to me eventually when he got his own. We lived as roommates for a long while and he had a profile on it with lots of saves.
A few months pass and he contacts me to tell me my system red ringed. And instead of trying to return it, or checking with me if the warranty was still good, he tossed it. With the hard drive still in it. HUNDREDS of hours of gameplay dead and gone because he didn't think it through. I still haven't really confronted him about this, it's not worth the time or aggravation in the long run. Still hurts like a ***** though, forced me to replay Dragonage Origins and Mass Effect and Mass Effect 2 all over again.
A newer case would be my PS3 getting the YLOD. And Sony in their infinite wisdom deciding that you can't transplant HDDs from one PS3 to another. So my 70 hours of Dragon Crown is gone, my 60 hours of Ni No Kuni is lost to the void, not to mention my host of downloaded PS1 games and access to PS2 games(it was the release model that did everything). That really stings, since I'm not going to be able to purchase a new system for a while and that won't bring back my backwards compatibility because they DROPPED IT FOR REASONS UNKNOWN TO ME!