BitFenix claims the case will support motherboards of the Mini-ITX, microATX, and ATX persuasions. Inside, you have almost exactly 12 inches of space until you run into the upper drive cages. Shoehorning an Extended ATX board into the Shinobi is out of the question without some modification.
The hard drive and optical drive were simple enough to install. When mounting the optical drive, you remove the tool-free lock by pushing on it. Then, line up the holes for the drive, and pop the locking pins into place. Installing a hard drive is a little more cumbersome but still fairly straightforward. There are two locking mechanisms per drive: one on either side of the drive cage. Knobs associated with each mechanism are turned counter-clockwise and then pulled away from the chassis, which can require a little wiggling. After that, you slide the hard drive into its slot and ensure that the holes on the case and drive align before replacing the locking mechanism. Once the pins are pushed into place, a simple clockwise twist locks the drive in place.
I must confess that the hard drive mounts felt a bit cheap. The locking caps sometimes twist off entirely, and drives that have been installed properly still exhibit a lot of play. Without a more secure locking mechanism, I'm leery of transporting a system built in the case for fear of drives shaking loose. Prospective buyers who picture themselves moving the Shinobi frequently would be better off ditching the tool-free drive mounts and using old-fashioned screws to secure their hard drives.
Subjectively, the case's internals feel open and easy to work in. The Shinobi can accommodate graphics cards up to 12.5" long if there are no hard drives situated directly behind the card. The Radeon HD 6870 used in our test build has a modest 9.5" circuit board length, which proved easy to accommodate. You can squeeze in massive graphics cards like the 12" Radeon HD 6990 if you're so inclined.