I can't tell you how much I like this idea. It's a library service that turns up books that are least likely to be associated with the ones you type in.
In other words, it does the opposite of what intelligent recommendation engines, from Amazon to iTunes, aim to do ('if you like this, you'll like that...").
In practice I'm not sure how much I'll use the Unsuggester, at least as it currently works. But it's the idea of it that I find attractive. The danger of recommendation services, and of the way that digital media is structured more generally, is that we all end up burrowing around our own rabbit holes, and rarely find ourselves sniffing the air in some unfamiliar locale, trying to work out what the hell this is all about. Which is bad, in my blog, because it stifles creativity. Now and again, we need stimulation from sources we'd never have sought out on our own.
(Discovered via the always-stimulating Sparkthinking)