InstaQuote - nice site that lets you log quotes that you like and autocompletes them as you start typing them in (with an interface similar to my site instadefine.com). Knowing the thread of quotes a person resonates with is a very powerful, and truly relevant dataset that gives you a window into their soul. You can use the data to introduce people who ought to meet each other. You can notice patterns in the progressions of quotes people like and fast-forward people's intellectual development by suggesting works that might interest them (e.g. people who like ayn rand, I notice, often later get into eastern philosophy)