Glue Ball and Compressor Stall,
What you guys are saying is true.
There is an aclimatization process that goes on. People who live at high altitude have a higher red blood cell count. The red blood cells are those who carry oxygen throughout your system. If these people were to go to live at sea level for a few weeks and then return to their homes in the high country, they would once again have to readjust and it would take a few weeks.
When the Olympics were held in Mexico City, the athletes who had lived and trained at high altitude faired better than those who lived at sea level.
As far as drug use (and for pilots I recommend using supplimental oxygen over smoking joints to deal with the high altitude flight environment), consider that the South American indians in the high terrain chew coca leaves (the same stuff that is used to produce cocaine) in part to deal with the high altitude environment.