diver, my undertanding is that all airlines do it. Typically one remains a member of elite on both airlines during that year, but the name of the game is maintaining that elite status subsequently, so hopefully if one switches, that person is trying to get to the highest elite level on the airline to which s/he switched.

If rjwx2man stops flying on United as he has said he intends to do, it would improve the upgrade the situation on United but make it worse on Continental. It is a zero sum game if equal number of people are switching. Now maybe rjwx2man wants to donate his pile of upgrade certificates to me?