Over the last month Google has made significant improvements to the Android Market app. Version 3.0 provides a much better user experience for discovering apps, and it adds the ability to buy books and rent movies directly from your device. Google is now rolling out an update to the Android Market app that adds an often requested feature, the ability to secure the app with a PIN.
Parents are probably the ones who need the PIN capability the most to prevent their children from accidentally buying games and running up their credit card bill. After you assign a PIN it will be required before purchasing applications.
Another new feature is the +1 button, which you can tap to indicate that you like the app. The +1 buttons have been available in the web-based version of the Android Market for a while, so this update brings the Android app on par with the web version. Keep in mind that the items you +1 are tracked on your Google profile, which provides a convenient way to access items that you like on the Internet. Unfortunately the +1 portion of your profile is not available in the Google+ Android app.
Google slowly pushes out the updates to the Android Market app over the course of several days and weeks, and in my experience the update occurs automatically, so you won’t know that you received it until you notice the new features. I think that Google ought to provide a notification on the phone to indicate that the Market app has been updated. Unfortunately, you will have to check the settings in the app to verify whether or not you have the updated version.