Thankfully, we have some very well informed and proactive friends that keep us up to date on all sorts of health and environmental concerns. They were the first to tell us we needed to switch out our old clay cat litter for something more healthful for our cat Rocky.
You may or may not know that clay litter contains silica that can cause respiratory problems in cats. (And, perhaps for the owners as they empty the cat littler into the cat box, and/or clean it?) This pertains to the non-clumping variety. If you think you can avoid it by changing to a clumping kind though, think again. In order for it to clump, the clay has added sodium bentonite. Liquid added to sodium bentonite causes it to expand to 15 times its original volume. If your cat ingests any of this litter while doing its grooming it can cause serious internal problems.
We switched to Swheat Scoop last year and our cat had no trouble adapting to it. It scoops and clumps well, and even though adding new litter periodically creates some dust, we (two humans and a cat) haven't had any adverse effects. There is a more in depth article on moderncat where you can get more information and read other cat owners comments.