I borrowed out BioShock for the 360 almost 3 years ago, still haven't got it back.
I poke the guy I lend it to about it every now and then, I only speak to him through MSN. He still didn't send it over, while I asked if he could do that this week.
I also have 2 games I borrowed from other people, Unreal 2 and Black and White 2 and I haven't spoken with both of them in years. That's 2 more to add to my game collection.