Yesterday I got my new grey card in the mail from Robin Myers Imaging. It looks visibly different from my old Kodak grey card. I took a test shot with the WB custom set to the RM card (bottom), but with my Kodak card in the photo as well. I though it would be interesting to go into Photoshop and see what the grey card from Kodak comes up as, when the RM card is white balanced. As you can see, they are visibly different. I've put the RGB values next to each card. You can see that the Kodak card is not neutral, and would result in a blue cast if used to white balance. Looking forward to doing some test shots with people to see the difference.
It is also much more durable - more plastic like and supposedly waterproof and washable. Price was about the same too, but the RM card is much smaller than what was in the Kodak package.