I found this article -
http://news.bbc.co.uk/1/hi/entertainment/6440981.stm - quite interesting.
Top Ten Unfinished Fiction (and my notes on some)
1- Vernon God Little, DBC Pierre
2- Harry Potter and the Goblet of Fire, JK Rowling
3- Ulysses, James Joyce (- English undergraduates probably comprise the majority here)
4- Captain Corelli's Mandolin, Louis De Bernieres (- probably because a large amount of non-readers bought it after seeing the film. Book is actually pretty readable.)
5- Cloud Atlas, David Mitchell (- I have read Ghostwritten and can understand abandoning his work, good but hard)
6- The Satanic Verses, Salman Rushdie (- again, I'd imagine non-readers bought because of the fatwa thing)
7- The Alchemist, Paulo Coelho
8- War and Peace, Leo Tolstoy (- doubles as a boat anchor)
9- The God of Small Things, Arundhati Roy (- was a bit of a fad, is decent though)
10- Crime and Punishment, Fyodor Dostoevsky (- one of those 'must reads' that isn't an easy read)
(There is a top ten list of unfinished non-fiction to be found at the link, it is much more British orientated though, although 'My Life' by Bill Clinton is at number two.)
Books I notably haven't finished -
A Suitable Boy, Vikram Seth. Falls into the
War and Peace length category at near 1500 pages. I also started
À la recherche du temps perdu like many people have. Made it half way into
Within a Budding Grove. I did finish Roy Jenkins' epic Churchill biography, didn't think I was going to make it.