It looks like Alikewise.com has been around all year, but I only heard about it this weekend - it's a dating website that matches people based on the books they like.
This is a great idea for a dating website - it seems a much better way to get at someone's true nature than filling out a profile by guessing what will make you attractive. I checked around the site a bit (without creating a profile), and wonder if there's a way to tie-in with sites like LibraryThing and Good Reads to capitalize on peoples' full libraries. LibraryThing sort of already does this, with their You and None Other meme.
But here's something funny: at my first library, we toyed with the idea of a "singles night" book group. We thought it'd be a perfect program for Friday nights, after work, to come and meet other single people interested in books. It never happened, but I always liked the idea. Maybe that'll eventually manifest in Alikewise meetups.
And wouldn't this be a heck of a social networking widget to add to a library catalog? "Like this book? Click here to meet other patrons that do, too."