What is about beer that inspires people to be so creative? Yelp recently held its second hackathon in which their engineering team was given 48 hours to "work on projects they think would be useful, funny or cool." One of the results was the iPad KegBot that combines an iPad, flow and temperature sensors, an Arduino (an off-the-shelf hackable hardware microcontroller), an RFID card reader, and a kegerator with taps.
In their own word: "It measures the amount of beer flowing, displays information about the beer, keeps track of who's been drinking via their RFID card, and measures the temperature of the beer." And not only does the iPad KegBot have a leaderboard, the thing is networked so you can check the status of the beer from a browser. And it's since it's from Yelp, of course you can rate the beer as well. Here's video of it in action:
Video: Yelp Kegbot