New Medicare cards are being mailed out, and I got mine today (apparently California is among the first states). The reason is to correct something I have complained about ever since I got mine almost 4 years ago - instead of showing your Social Security number as a large part of your Medicare number, your Medicare number is now completely unrelated, thus helping to protect your identity from theft.
I am also glad to report that the cards are no longer just a little bit too tall to fit into regular wallet credit card slots. That was my other beef.