You know, maybe a more interesting question would be does anyone use the ZS as AA laid it out.
I've been browsing his three books (The Camera, The Negative, The Print) and I find he is probably one of the most technical photographers I have come across. I also recently got The Book of Alternative Photographic Processes by Chris James.
Comparing the two is interesting. While Adams goes for a very technical, very precise methodology, James goes for a more free-flowing experimental style. While both give you formulas for doing various things, Adams tends to focus more on precision and exactness. James literally says for some things "Just play around until it works for you".
While it may not be fair to compare the two directly considering content, history, etc., I think this illustrates how different people work.
Some people are very technical. They want a mechanical precision to their work. Repeatability. Perfection. Definatly Adams in a nutshell. Most of his work is done in LF with very good lenses (or the best he could get at the time). The plane of focus is sharp throughout the image. You can almost cut yourself on his images they are so sharp.
Others are more 'philosophical' about things. Like James. Most of hsi work that he presents in his book is done on a Holga. When he makes a print he tends to go for visceral feeling instead of technical perfection. While he knows his forumlas and processes, he is not a slave to precision. If it works it works. If it is reapeatable that is better, but he seems more focused on the end product.
How does this relate to the ZS? Well, I think people use the ZS differently too. There are some technical perfectionists who really use it. They take copious notes per exposure, they develop accordingly, and then will spend hours and hours making sure a single print is absolutely perfect. Others, like myself, will take what they can from the ZS. I am sure to Adams I am almost abusing his system in some ways. I think about the ZS for maybe a few seconds for the exposures that I use it on. Sometimes I barely use it! I simply have a vague notion in the back of my head as to what will be in shadow, what will be in the middle, and what will be in the highlights. I've used it on color slides even. I tend to pick it apart and use it as it suits me. Which probably places me more in the James camp. People like him are more concerned with the outcome. In the end the question is not so much is the ZS relevant, but how is it being used. The ZS as Adams wrote about it is probably relevant to very few people. The ZS as a tool which we can mold to our individual uses is probably still very relevant to most serious amateurs.