Does Shopping Cart Advertising Work?

We were called today by a salesperson regarding advertising on shopping carts at our neighborhood Vons Store in Camarillo, CA.  We have great exposure on the internet on page 1 of all the search engine results pages for local Ventura County searches, but the shopping cart advertising program seems like it would be a good tool for bolstering our local branding efforts.  Are there any Realtors out there who have any experience with whether or not shopping cart advertising works.  Is it worth it?