[ubuntu] Virtualbox will not go full screen in 12.04

There are many threads on this topic, but no fixes and all are old threads. Perhaps there's some new info? I just installed the latest version of VB and it works great. BUT I cannot get VB to go full screen in 12.04. I've read about installing Guest Additions, but there seems to be much confusion about that, too. Is there any recent info on this that suggests a fix?

Thanks for considering this!