Man, this page has way more information that I've ever seen in one place about the Centurion Card. Click Here to read it.
I've tried downloading that page so it can be preserved in case it gets nuked from geocities, but all I've been able to do is get all the pictures. The source code doesn't come up for me and the html file is useless when I download the whole thing. If anyone has better skills at this kind of thing than I do, then go for it. It really is good info.
Among some of the more interesting facts on that page were the pictures of the titanium card compared to the plastic card. Here is one where the plastic card is on top and the titanium is on the bottom.
You can see how the words 'American Express' are different sizes. That should help anyone to spot the difference if you are looking to buy one off ebay or somewhere. Don't believe them when they say it is a real titanium card if the words aren't small. Also, here is a neat picture of the side of the card showing the thickness.
And the real proof is right here. What is different about the back of this card? (other than the japanese writing)
You won't see any reverse number imprints on the back of a titanium card. I don't know how they do it, but the numbers are raised on the front and it is perfectly smooth on the back.
I can take pictures of the card I have if anyone wants to see anything else on it. It is a promo card and not a real cardmember's. In fact, it has the same card number as the JL Benjamin card on that website. It says it expires 06/09 on this one, so maybe I'll play with it for a few months still and then throw it out on ebay or something.
You would be amazed at what flashing a black card (even when it doesn't have your name on it) can do for you.