Re: Who here has tiled their floors?
In JBIV, I used 6x6 porcelain tile, that looked like slate, on a good v-troweled thinset bed (I used Bostik 2200TS, a transportation-grade adhesive). This adhesive provides a tough, flexible bond ("tenacious bond" per the specification sheet). Also, it doesn't break unless stetched about 200%. Originally, JBIV had 12x12 ceramic without a good thinset bed, so the large size and lack of distributed support resulted in many cracked tiles.
In the current install, I have just seen the first 2 tiles crack after 7 months, but it is apparently the result of someone really stomping the hell out of one (while the other had a corner cutout). Even so, it is difficult to see the cracks. So difficult to see the cracks, that I'm not worried about replacing them, indefinitely. I tested one tile before installing them by wedging it under the jacuzzi that I had just removed, and lifted the jacuzzi up, and the tile didn't break or crack. So, as said in an earlier post by lornaschinke, porcelain is very tough.
I wouldn't do natural slate if I were you. Very brittle stuff.