I'm sorry I should have been more specific. I know that the promotion runs until Dec 31 1999, but what is the expiration date for the airline certificates that they mail, after you send them the receipts and proof of purchases. In other words what is the latest that the airline mile vouchers have to be turned in to the airline (say Delta or United)?

For example, the MSNBC vouchers are good until sometime in 2000, so I am planning to mail my MSNBC United voucher next year and not this year, since I don't need the miles right away and United miles have a 3-4 year lifespan.