My brother has a different set of lending ideals than I do. I lend very little to very few, but be lends a whole bunch to people I haven't even met before. The trouble starts when siblings have to share property they were given for birthdays and christmas, gifts that were adressed to both of them. In my case, this meant that if it was belonged to both of us he had free access to lend it in any way he saw fit. It got pretty fraustrating when you got an itch to play a classic in your library and it turns out to be at some bum's house.
Most recent episode of that was when my brother started hanging out with this older 'frat boy' type of guy from a nearby town. This guy had a reputation for being trouble, but my older brother is part hippie now and he claims to accept everybody. The new guy had just come off a construction job and decided on a whim to buy an xbox and about $300 worth of games and equipment. Of all the games he bought, he didn't buy Halo 3 which my brother and I owned a copy of. My brother lends it, once again without my knowledge. About two weeks later I heard down the grapevine that he had totaled the disk. The way it was decribed to me, he pulled off a classic noob manuver and tilted the console while it was in play, sawblading the disk to worthlessness. He got up with my brother later and told him about the damages promising to buy him a new one... after his income tax return came in anywhere from one to three months later. I got impatient with deadbeat and went out and bought a shiny new copy for myself. If we were to ever get a new copy back from deadbeat it would belong to my brother and he could lend it out to as many bums as he wanted. About two weeks later my brother got a replacement from the guy. It wasn't a new disk however. He gave us back our old case and manual with a new used disk with plenty of wear. Upon further investigation it turned out that the disk was stolen from his neighbor.
So yeah, I don't lend out games myself. There's too much risk of not ever seeing them again.