Yes, it's worth another post - I hadn't heard that theory before.

::runs off to do some Google searches::

Some difficult work with Google revealed that the technical term is the "sociometer" theory - and it's fairly recent (the oldest citation I see refers to 1995), which would help explain why I hadn't heard of it before. It seems consistent with my personal experiences, so I consider it credible.

For more information:

http://www.psychwiki.com/wiki/Sociometer_Theory