The app is available for Apple devices as well, so you can use it to share things with a friend's iPhone as well, for example.
Other apps are also integrating it in to their own apps as well, such as PayPal uses Bump to send money to someone via your phone. You can launch the PayPal app, then bump your phone with someone elses to send them money.
It's a useful app if you often share things with friends. Easier than having to setup a Bluetooth connection. The app can be found in the Android Market by simply searching for "Bump".