The Centerpoint script shows up in the Plugins Menu.
This script can be used to place a construction point (a small "+" sign) in the middle of your selection. This can used as an inferencing point or measuring point for other actions.
To use the script, first select an entity or entities and click Plugins>Set Center Point. A construction point will be placed in the middle of the active selection. (This means if you editing a group or component, the construction point will be part of the group or component.)
July 21, 2006: Enhanced CenterPoint to look at the whole selection and place the construction point in the middle of the entire selection. The previous behavior only looked at the first entity in the selection list. The current version is now v1.2.