Kathleen has posted another video showing the VSTO 'v3' CTP and how to create a VSTO add-in that creates a ribbon for Access of all things!
There's still a bit of rocket science involved here--in the final version of VSTO 'v3' we'll make it much easier and more "RAD" to create and modify ribbons. But this should give you an idea of how to start playing with ribbons now.
As I'm sure you've noticed, the VSTO 'v3' CTP requires the Beta 1 Technical Refresh of Office 12. This beta isn't widely available, but there will be a Beta 2 of Office 12 that will be more widely available. We plan to refresh the VSTO 'v'3 CTP to work against Beta 2, so if you haven't tried out VSTO 'v3' and Office 12 programming because of availability of Office 12 Beta 1 Technical Refresh, don't worry--you'll have a chance to play once Beta 2 comes out.