Trying to dig up more info on a crush, a new friend, or a potential employee? If you want to employ all the detective opportunities the Internet affords you, download the Firefox extension Identify.
Once you've downloaded Identify, go to anyone's profile page on a social network, like a Twitter or Facebook page (it seems to work better with Twitter), and press Ctrl + i. Aggregated info posted about the person on the Internet shows up in a popup on the page.
It's not exactly sneaky, since it's all info that's readily available, but it feels pretty sleuth-y. Want another spy tip? Learn how to follow people on Twitter secretly.