I wonder what is the advantage of using Fragments(the new version of ActivityGroup) As for now I can do the same with TabActivity. If I want to replace the fixed tabwidget I can set visibility to gone and to change tabActivites I can use setCurrentTab(int c) in the onClick event of my custom layout. Could you tell me a motivation to use FragmentActivities instead?
TabActivity is depricated. See here: http://developer.android.com/reference/android/app/TabActivity.html
In my opinion the transition towards FragmentActivity is a good move for the community, offering a simpler designed approach to "fragmenting" activities and the views they contain.