If you like books and statistics, you’ll love LibraryThing. They have 554,277 members who have cataloged 33,647,263 books of which 3,850,295 are unique works not shared by anyone else on the site.
Harry Potter and the Sorcerer’s [Philosopher’s] Stone is owned by more people than anyone else (37,254 copies, 3 of which are mine), although more people have posted reviews of Harry Potter and the Deathly Hallows (704 reviews, with an average rating of 4.43 stars out of 5).
Oh, and one more thing (which is actually the whole point of this post): The Book of Mormon is at the top of a list based on another site-wide statistic. Care to guess what that statistic is?