AppBrain provides a platform from which to discover new apps and share your apps with other users. More than that, you can also find your apps on the website and sync them with the Android app. It can also tell you if you have any updates, and if so, will go to each app in the Market and update them.
The new update has given AppBrain a new UI, beginning with the home page, which now consists of 4 icons, rather than the previous list of several links.
The previous version allowed you to see the other user's lists, but with this version, they have gone a step further and added some social features.
You can now add people and "follow" them or search for users. There is even an option to connect to Facebook and add your friends who might be using AppBrain. Also, there are a few well known faces on the popular users button, such as Leo Laporte and Gina Trapiani, who are number 1 and number 2, respectively. You can then follow them and look through their list of apps. If you are not the following type but would like to share your apps with others outside of AppBrain, you can email, SMS, or send through twitter.
AppBrain now makes app discovery much more friendlier by making it socially popular to add people and follow their apps. This will certainly allow you to discover for yourself what other apps are out there.