I got the following email from e-Rewards. Same message appears on my e-Rewards "home page." Have you taken a look there?

IMPORTANT NEWS ABOUT YOUR REWARD CHOICES

During October, the Northwest Airlines WorldPerks® program will officially merge with the Delta SkyMiles® program into one frequent flyer program – Delta SkyMiles. To learn more about the merger, please click here.

Although WorldPerks® and E-Certs will no longer be available as a Reward choice, we are excited to inform you that you will be able to redeem for Delta SkyMiles® effective October 1, 2009. Please continue to check your e-Rewards home page for updates regarding this program merger.

To redeem your unused e-Rewards Currency for Northwest Airlines Rewards, please click the button below to visit your Rewards Center:

Also, be aware that the terms for redeeming e-Rewards points on Delta are a bit different than what was possible when redeeming for NW miles. NW's offer let you redeem once every quarter. Delta will only let you redeem once every 180 days.

Given that, you might want to refrain from submitting for smaller mileage amounts (500, 1000) and save up to redeem at the maximum mileage level (2000) as otherwise you'll be locking yourself out of 50% of the miles you can throw at your Delta account via e-Rewards redemptions evey year.

Best,
TMichaels