I've been using Untappd for a few weeks now and I have to say it is one of my latest addictions. It can simply be described as a "foursquare for beer drinkers" -- a social network allowing you to share whatever brew you're drinking with your friends. Untappd works only via the mobile site (untappd.com) on devices running BlackBerry OS6. Sadly only the WebKit browser can handle the mobile site for now, but hopefully a native app or slimmed down mobile version will be on the way down the road.
To use Untappd just setup your account, login and you're up and running. Search for whatever beer you happen to be drinking at the moment, then check-in and tell your friends. You can add a location (home, bar etc) with each drink, but unfortunately the BlackBerry GPS doesn't play too nice with Untappd, so getting this done works about 1% of the time. For this Untappd uses the foursquare API and pulls from the same locations. Earn badges as you go for completing various tasks and share your winnings and brews with friends on Facebook and Twitter. You can also comment on your friends drinks as well as toast them. Kind of like being there at the bar while not really being there at all.
The web app is very well done and pretty much eliminates the need for a native app, and OS 6 users can even add the bookmark to their homescreen to kill the feel of using a mobile site at all. Untappd is free to use and you can sign up from the web or mobile at untappd.com.