Just picked up a new 2010 CX-9 with the cargo tray installed. djjr50's pic is accurate. Comes in 5 sections: one across the floor of the cargo area behind third row seats, and two each on the backs of the split row third row seats. When third row is folded, the sections on the seat backs are now on the floor, and the extra bits cover the crack between the third-row seat backs (now folded down) and the rear cargo area. The overlapping sections of mat mean that it's not watertight, but still useful and better than carpet.
They're held onto the seat backs by velcro, so if dealer hadn't "installed" these, it looks to be trivial to DIY.