I just added the "share" feature to my Party Light app, it was easy. The actual code is only a few lines. When you click share in the app, it allows you to share with any services you have registered on the phone, email, twitter, facebook, etc. I learned how to do it from this page: http://labs.emich.be/2010/01/23/how-to-send-to-twitter-or-facebook-from-your-android-application/
Well, one thing you could do is get the official facebook app, then open it and post an update about the app you like.
Also there is an app that will do just what you asked for... It's called AppAware. What it does is keep track of what apps you install, uninstall or update, and it keeps track of top apps. Other people with AppAware can see which apps are on top of the list. To share your apps on facebook, open AppAware, tap the "installed" icon at the bottom. A list of your installed apps will appear, then long click (press and hold) on the app you want to share. A menu will pop up that will let you share it on facebook.
— modified on Jul 19, 2010 6:52:12 AM