Thanks guys :)

Michael - yes, I guess I was thinking that each object could have a local axis, with a "center point" - which would, by default, be the center of the whole object, but you could also move it to any other point on the object.

Having a centroid, as you said, in the exact center of the object would be handy - I'm often needing that, and the BoundingBoxCenter command is a little bulky to use (and then you need to delete the point, etc.)