Instead of checking in to a location (though you can do that too, if you link your existing Foursquare account), you check in with what you're watching. Miso keeps track of your check-ins and rewards you with badges relating to specific genres (and sub-genres) of film and television. Link your Twitter or Facebook, and suddenly, you're posting what you're watching with friends and seeing what movies they're watching as well. Genius.
I was already sharing my personal viewing habits via Twitter anyway, so Miso has been especially useful in that regard. The app is still a baby (just a little over a month old), and the folks at Bazaar Labs aren't done tweaking the features yet. There are still some obvious needs with the app, like the option to rate what you watched or apply genre tags to titles that Miso doesn't recognize (would've been useful when I was watching Four Sided Triangle earlier today). If you're a die-hard movie geek, this app is a must-have.
You can download the iPhone/iPod app at gomiso.com and follow @gomiso on Twitter for updates.