I am guilty of taking a long time to return borrowed books because I'm busy and have a lot to read, but keep borrowing, and sometimes buying, more than I really have time for. I always do return them eventually, and in the same condition I borrowed in, but I take ages.
I loan them to people, and once in a while I lose one that way, so I wouldn't lend anyone a book that it would break my heart to lose.
I do lend books, but more often than not, they never return, and I forget which book I had given to which friend. On the same token, books end up in my shelves and I have no clue who they belong to. Oops.
I don't 'loan' books, CD's or DVD's. That way, I don't lose them!
Conversely, I will accept a loan of books or DVD's from one, & only one, friend. There's no 'time limit' placed by her on the loan, BUT I ensure I return item to her the next time we meet, which is usually about every three months.