Pinning an object to a vertex

I needed to pin buttons onto a deforming shirt and as I didn't want to simply skin the buttons to the armature, I needed to constrain them somehow.

Michael W at blenderartists pointed me to this gem from the 2.4 Wiki...

You can parent an object to a single vertex or a group of vertices as well; that way the child/children will move when the parent mesh is deformed, like a mosquito on a pulsing artery. In Object mode, select the child/children and then the parent object. ⇆ Tab into Edit mode and on the parent object select either one vertex that defines a single point, or select three vertices that define an area (the three vertices do not have to form a complete face they can be any three vertices of the parent object), and then hit ctrl p

~Glenn