A neat item that I stumbled upon while reading about the most recent VirtualBox maintenance update is that the VirtualBox wiki page now contains some sweet little video tutorials that are called VirtualBox TV (or, alternatively, The Fat Bloke's Shorts). A variety of videos are available, and I will include one of them in this post. It involves enabling 3D acceleration in an Ubuntu guest session.
There are also links to live product webinars which are longer, but filled with good information.
I'm embedding the most recent webinar from August of 2009 discussing new features from the 3.0 release.