AGDee, my chapter uses a "Pi Society" program, too! We have a little ice cream party or something for all the girls who achieve over a 3.14 in any given semester.
As far as the GPA question goes with schools which are "tougher" academically, I attend
Hillsdale College, which I consider to be an extremely difficult institution. However, my chapter GPA last semester was 3.394 - the highest of any active sorority on campus, I might add.
Our chapter GPA goal for the past few years was 3.3 and we have recently (this year) raised it to 3.4 since we were consistently making a 3.3 and wanted something higher to strive for.
I think that internationally, all member of a Greek organization should strive for the highest academic achievement possible. Additionally, if they organization were to let those members taking harder classes or studying at "harder" institutions slide, that would be holding its members to a double standard.