Measure the Twitter & Foursquare Influence of the People Around You
Who's the most important person in the room? Candidates is a utility that allows you to pull up any Foursquare venue and get a readout of how influential (online) the people checked into that venue are. The site uses a proprietary analysis of Twitter and Foursquare usage to measure each person's reach. Do they have countless followers repeating their every insight? That's influence. Are they howling into the void? That's not.
Social media marketing means targeting these "influencers": finding the one person whose endorsement leads to a cascade of online mentions and purchases. This is a great tool for finding those influencers. (But be careful! An "influencer" who doesn't like your pitch can do a lot of harm to your reputation.)