With the tile search completed, the guys started prepping the floor. The floor immediately above the floor joist is OSB, which isn't what you want under the cement hardibacker board. To prevent bubbling from moisture, the hardibacker should be installed on top of an exterior grade plywood. The cement board is installed on top of the plywood with with thinset and screws. This makes for a very solid floor which is important because we are using 18x18 porcelain tile. Flexing in the floor could cause the tile to crack.
Here are a few shots of the finished subfloor. You will notice that the seams haven't been taped yet in these pictures.
Here's a shot of the tile in the laundry/mud room. The lines look to be nice and straight :)