Posted for "Rick Lafford" <gliderguy89@earthlink.net>:

 Art,
 
For ground operations, regardless of altitude, I pull the mixture until the
 idling engine stumbles and the enrich slightly. There is really no way you
 can hurt the engine by leaning too much at idle and in general, you'll do it
 a whole lot of good. The important point is to be sure that there is no way
 you can forget and try to depart with the mixture leaned incorrectly. Not
 that I'd ever do such a thing.
 
 Rick Lafford
 Dansville, NY
 
 You'll have to ask Scott for a more balanced opinion.