This offer is via FW:

As a valued Mileage Plus® member, you are invited to apply for a Mileage Plus Visa ®1 and soon see your mileage balance grow.

As a new cardmember, after you spend $250, you’ll earn 21,000 bonus miles2 and a $200 gift card to use at any of the 78 worldwide locations of Morton’s The Steakhouse3. Enjoy a spectacular dining experience with exceptional hospitality and service.

You will also enjoy these Mileage Plus Visa benefits:
Earn one mile for every eligible $1 in purchases4
Exclusive cardmember redemption opportunities 5
Earn travel certificates after first purchase 6
No pre-set spending limit 7
Apply by April 30, 2008!

A description of the gift card offer can be found here, though neither of those links specifically mentions the number of bonus miles that will be awarded.

Edit 10/22/2010: This promo is no longer available. Current United Mileage Plus credit card offers can be found here:

• United Mileage Plus Select Visa offer
• United Mileage Plus Signature Visa card