Has anyone read the following in the One Pass Member Advisory and what exactly is the Mileage Plus 18 month expiration policy?

Mileage Expiration
Miles currently have no expiry date; however, Continental Airlines reserves the right to impose expiry limits or terminate the OnePass program, thus terminating your ability to claim rewards. The OnePass program will formally end on December 31, 2011, followed by a wind-down period during the first quarter of 2012. Following the wind-down period, your OnePass award miles will be replaced with an equivalent grant of Mileage Plus reward miles. At that point, the Mileage Plus 18-month expiration policy will apply.