United is giving 500 bonus miles for any donation greater than $50, and double miles with their Visa card

Member Contributions Rewarded by United and Chase Bank
Any Mileage Plus member who contributes more than $50.00USD or equivalent to one of United’s designated charities by January 31, 2005 will receive a bonus of 500 redeemable miles* (see Terms and Conditions). United will contribute up to 5 million miles to support this bonus mile offer. In addition, Chase will award double miles** (see Terms and Conditions) to any member who uses the Mileage Plus® Visa® card to make their donation. Chase will provide up to a total of 5 million miles to support this double mile incentive.

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