I used these several years ago when I had my Rottweiler, and they worked wonders. He loved to chew on them, and they did an incredible job cleaning his teeth. In fact, during the 8 years that I had him, I never had to have his teeth professionally cleaned. I'd give him a ring to chew approximately once a week. With that said, they do make quite a mess, leaving chunks of "polishing paper" scattered all over.
I have been unable to find these for the last couple of years, and it does look like the design is somewhat different than they used to be. But now that I can find them on Amazon, I'm going to order some more and see how they work on my Bullmastiff.
Edit 05/18/2012: So I've tried several packs of these, and I have to say that the "new formula" is nowhere near as good as the originals were. They still work okay, as my dog likes to chew on them, but I just don't see the same amazing results that did with the original product. Such a shame, because the originals worked so well.