We all know how difficult it was to customize (or personalize, if you prefer) Office 2007. That changed a lot in Office 2010 and everything has become much, much simpler. A major change in this customization of the Ribbon is related to the scaling of groups. Previously, only the standard groups in the Ribbon could collapse. Now, Microsoft introduced the autoScale attribute, which is used to determine if a custom group should or should not collapse when we reduce the size of the Ribbon or the resolution of the screen is reduced.
Check out the picture below (I am actually using Office 2010 in Portuguese, but you will get the picture, if you forgive me the pun):
Figure 1: A Ribbon custom Group expanded
The group "Minhas Ferramentas (My Tools)" at the moment is expanded as usual. But assuming that the configuration of your screen or monitor is changed, you would get the following result with the autoScale set to "true" (autoScale="true"):
Figure 2: Custom Ribbon Group collapsed
If we keep reducing the Ribbon, the group is continuously reduced in size, and it further collapses the elements of our group:
Figure 3: Buttons collapsed to a splitButton
To implement this customization / personalization of the Ribbon just add the attribute autoScale and set its value as "true". Note that this attribute must be determined for each group separately, it does have a global effect on other groups in the Ribbon.