How to add a tabbed menu on group main page (panel)?
I got a working and straight solution (tabs are panel style) using panels_tabs.

panels_ajax_tab seems more nice (and more clean from a designer point-of-view), but it is also more cumbersome as it only accepts mini-panels as tab elements, and then I'm not sure how to pass the group information down from the main panel to the mini-panel and finally the embedded view panel.

Further panels_tab load all the page at once and then just hide the unused tabs, so if too many views are loaded the page can take pretty much long time to load !