You have to sign up online or by phone. Goes from April through June. $1500 purchase limit (some stores let you get up to $50 cash back w/purchases which is processed as a credit charge.)
http://www.discovercard.com/discover/data/cashback/cbbpromotion.shtml
"During April, May and June, Discover® Platinum and Classic Cardmembers who participate in Cashback Bonus® Programs can get up to 10% back on qualifying grocery purchases. You?ll keep earning up to 2% back on other purchases, too.
You need to sign up in the Account Center to get this special award or call 1-800-475-9161. Then, pay with your Discover Card and we?ll credit your special Cashback Bonus award to your Cashback Bonus Account. But remember, you have to sign up to receive this special award.
Cardmembers enrolled in this offer will receive up to 10% Cashback Bonus award on grocery purchases and up to 2% Cashback Bonus award on other purchases when cash award is exchanged for up to double the amount in certificates from our Cashback Bonus Partners. Cardmembers receive a cash award of up to 1% of each purchase based on annual level and type of purchases, plus Cardmembers enrolled in this special offer will receive an additional Cashback Bonus award of 4% of each purchase made with the Card between 04/01/04 or the date on which the Cardmember enrolls in this offer, whichever is later, through 06/30/04 at qualifying grocery stores, subject to a cap of $1500 in grocery purchases. Only Discover Platinum and Classic Cardmembers who participate in the Cashback Bonus program are eligible for this offer. Cashback Bonus redemptions available in $20 increments.
Not valid for grocery/food purchases made at Wal-Mart Neighborhood Markets, specialty food stores, convenience stores, gas stations, warehouse clubs, supercenters or discount stores."
http://www.discovercard.com/discover/data/cashback/cbbpromotion.shtml
"During April, May and June, Discover® Platinum and Classic Cardmembers who participate in Cashback Bonus® Programs can get up to 10% back on qualifying grocery purchases. You?ll keep earning up to 2% back on other purchases, too.
You need to sign up in the Account Center to get this special award or call 1-800-475-9161. Then, pay with your Discover Card and we?ll credit your special Cashback Bonus award to your Cashback Bonus Account. But remember, you have to sign up to receive this special award.
Cardmembers enrolled in this offer will receive up to 10% Cashback Bonus award on grocery purchases and up to 2% Cashback Bonus award on other purchases when cash award is exchanged for up to double the amount in certificates from our Cashback Bonus Partners. Cardmembers receive a cash award of up to 1% of each purchase based on annual level and type of purchases, plus Cardmembers enrolled in this special offer will receive an additional Cashback Bonus award of 4% of each purchase made with the Card between 04/01/04 or the date on which the Cardmember enrolls in this offer, whichever is later, through 06/30/04 at qualifying grocery stores, subject to a cap of $1500 in grocery purchases. Only Discover Platinum and Classic Cardmembers who participate in the Cashback Bonus program are eligible for this offer. Cashback Bonus redemptions available in $20 increments.
Not valid for grocery/food purchases made at Wal-Mart Neighborhood Markets, specialty food stores, convenience stores, gas stations, warehouse clubs, supercenters or discount stores."