For ALL the tabs ( default tabs and customized tabs) that are used in groupviewtabs and profileviewtabs -

There should be a html field that can be used when there is no content available after clicking a tab.  Now what we get is either a blank area or "Items not found".  I would very much like to give users a simple guide or link or whatever so they would know what to do with that tab. This backup html field only shows when a certain tab does not have any content.

Or is this something can be done already?

This is currently managed within the RESX files for your portal. Each control that is called can basically show a "no records found" when nothing is there. These can contain whatever you want and are managed by creating localized versions.

That said ... it would nice to have difference RESX files for each journal type, etc. For exactly this reason.

+1 ... it would be good to have unique information there informing the users of action points, how to add friends, how to use the event calender, etc.