Last year when Shoprunner was offering a FREE one year membership, I jumped on it, although, I have used Shoprunner over the last year, I rarely use it as there only 50 participating stores that offer Shoprunner at checkout.
That being said, I do recommend that if you are not a member of Shoprunner, sign up for the FREE Shoprunner 6 months membership!!! You never know when this service will come in handy. For example, Toy R Us does participate with Shoprunner.
Also, if I remember correctly, they do ask for a credit card, and I used a gift card with 1 cent on it and it worked perfectly!!!