There is often a need to center a model to the world 0,0,0 coordinates. Sketchup does not have this feature built in, so I searched the web for a solution. I found this little gem of a ruby script that almost does the job.
The plugin Center_Group_Bottom was found on a forum, made by someone named Dick.. Thanks Dick.
The original script centers the model in world, but places the model on the "floor", which is great for buildings and such. I changed the script a little, so the model is centered along the Z axis (up-down) as well. This change is needed for most models used in a game engine, such as balls, guns etc.
There are 2 scripts. Center_Group_Bottom, and Center_Group (my little change)
Unzip the little file, and place both scripts in your Sketchup plugin directory.
Once you model is ready, select everything and make it into a group or a component.
From the plugin drop-down menu, select the desired plugin, and it will do it's job for you.