I love the M40 case. It has easy access to everything due to the Two Layer design. The PSU needed for it is best to use something 144mm or less, as seen I use OCZ and they fit perfectly in it. I used a PSU that was 158mm long and it barely fit, but it did none the less.
Even with only 1x 120mm intake and 3x 80mm outtakes it gets plenty of airflow. It does have a spot for a 60mm fan in the top layer, but it requires removing the small LCD screen.
Installing everything was easy even in such a small case. I have had no troubles installing anything I use in it, and have found a way to hide all unused wires, and a way to route those I do use to out of the way spots.
Overall it is a very easy to use case when installing, cleaning and accessing, and can fit anything you really need.
Pictures are worth, oh who cares, easier to show how nice it is this way:
Top view
Side view; Front of case to the Left
Side view; Front of case to the Right
For anyone who wants an HTPC or just a small case for ease of moving and whatnot, I would recommend it.