I usually only loan to my cousins -- and I know where they live! (j/k -- well, I do know where they live, but we constantly riffle through each others' collections anyway, so it doesn't really matter. I could always just "borrow" it back if it's been gone a little on the long side). I do, on occasion, loan out to others with the hopes of having my books returned to me, as I am usually fairly timely in returning the ones I borrow (my momma raised me right!), but I realize it probably won't happen, and am pleasantly surprised on the occasions they are returned.
I've already had to replace one of my books (HP7, actually, which I wasn't too happy about, but what can you do? I'm just anal and have to keep my collection complete.) because of a "loan" (more like gift), and a few others are still missing, but I haven't seemed to care so much about their loss, so yeah.
I just lost another. The Giver, by Louis Lowry. Can't find it anywhere; no clue who I loaned it to. Darn it.
Lol. Well I hate lending books but Im just like you when I get a good read I want to tell the world about it. and let you read it if you don't have your own..BUT. I do get my books back.. Im a hounddog. I have this paper that I make people sign out with my books. They have to put thier phone numbers and address so I can knock on their door if need be.. lol
My friends think Im crazy with it I say no, Im just determined to keep my library alive!
I sometimes lend books to friends, but I always get them back. I also return every book I borrow. I think it's very rude to keep things that were not gifts.
What I do is keep a list of what I lend and the person who has the book. It's not that I don't trust my friends, it's that otherwise I would probably forget they have my books.
I've had some nightmares cases of loaning to friends. I've had books returned with no covers, pages ripped, books returned that have looked like they've been dropped in a puddle. I even had one book returned to me by someone who highlighted words with a magic marker. Another person returned one of my books to me and had written in it "property of...." and her name.
I had a housemate, without my permission, loan out of all Vampire Chronicles to one of her friends and I never saw them again. And of course, I've loaned books out and never seen them again.
These days I don't loan them out as much if they are my favorite books but if they are books I already have on my kindle then I'll loan them out and not be fussed if I don't get them back. A lot of my friends are slow readers though so I have a rule to never loan our books I have not read yet because it means I will wait forever to get them back. I had one friend who I would go bookshopping with and as soon as I bought a book she would want to borrow it but then would take 7 months to read it.