This is an offer that I took advantage of thanks to a heads up from a friend! (Thanks Pat!)
Fly between Chicago and Hong Kong between now and January 31, 2012 and you will earn double the award miles (base miles only, Class of Service is not considered). This applies only to United Flights 895 and 896, both 747-400 non-stop flights.
Chicago to Hong Kong and return is 15540 miles, with the promotion, it becomes 31080 award miles. Just remember that these miles do not count as Elite Qualifying Miles, but otherwise a great way to increase mileage balances in your Mileage Plus Account.
To qualify, you have to register HERE. Be aware of the terms and conditions as only certain Fare classes (F, A, J, C, D, Z, Y, B, M, U, H, Q, V, W, S) are eligible for the bonus miles.