Hi Michael,
in sketchup "groups" are named objects and "components" are instances.
They are quite powerful.
If you edit one component (double clicking on it) and save it all other copies are updated. You can "save as" a component in an external file; "reload" a component from an external file (changing all the instances); "make unique" a component so it is detached from all the other copies. You can also add or move sub-components or sub-group using the "Outliner" tool.
In Sketchup pro 2014 it is also available a "Classifier" tool: you can attach info to a component for exchanging data (not only geometry) with other 3D BIM software or for extracting data and to generate reports.

Thank you for your great work!

-Giovanni