Here is an excerpt from an email I received.

As a Mileage Plus(R) Premier(R) Member, you can help make every flight count for America's athletes.

It's easy to show your support. Simply register at:
http://www.united.com/moments

You'll earn double miles for yourself on every qualifying United roundtrip you fly between July 1 and August 31, 2000.

You will also receive a $25 Savings Certificate good toward a future flight when you sign up and fly a United roundtrip in any class of service, now through
August 31, 2000.

Best of all, United will donate Mileage Plus miles to the U.S. Olympic Team sport of your choice! With your help, we can reach our goal of 25 million miles.