I buy books very seldomly ( I'm one of the few persons at work my age *ehem* who still go to the library regularly) so my rule has always been, if it's cost me then it will get read, come hell or high water. I don't read all of my library books, but that doesn't prey on my conscience quite as much . Of the 25 books listed on the site, I've only read one, The Almost Moon. But I understand why it would be in this list although I loved, loved The Lovely Bones.
In my own personal list of unread books, I have The Little Friend by Donna Tartt (I haven't been able to finish it, after a year in my book pile); The Kite Runner by Khaled Hosseini (everyone seems to have read and loved it); the second book in the Twilight series (I forget the name, hmmm, but I just can't seem to get past the first few chapters before wanting to scream); and The Angel's game by Carlos Ruiz Zafón, no matter how much I liked The Shadow of the Wind.