Interesting. Just received an offer for double miles on NW in the snail mail. Includes flights and all partners; you get 500 miles just for signing up. Naturally I signed up. Then I tried to sign up my wife - within seconds I got this message:

We are sorry, the WorldPerks number entered is not eligible for this promotion. This offer was created specifically for the WorldPerks member who received the promotion and only the WorldPerks number listed on the promotion piece may be registered. The offer may not be transferred to other WorldPerks members.

Thank you for your interest and click here for other promotional opportunities.

Seems like USAirways web coders could stand to learn something from the fellows in MSP. Naaah, they're response is "Thank you for registering", "Push 1 to register for more bonus offers or *D to exit", send you emails congratulating you for registering, award the miles to entice you to buy more tix, then post anonymous messages through 3rd parties basically accusing their VFF's of being criminals.

Ya gotta wonder.