Installation, drives
This hole in the drive bay chassis is in fact the hard drive bay. Like many other SFFs recently, the hard drive bays are rotated 90 degrees. This may have been done to reduce the amount of cable clutter that would have built up under the optical drive.
Adding a second hard disk will rotate the mounting 90 degrees
After your main drive, it is still possible to add a few more drives. In the bay above the HDD, you can install any 3.5" item such as an external flash card reader or hub. Since there is a second optical drive bay, you should feel free to buy a cheap 3.5" to 5.25" bracket for hard drive #2.
Now you see the problem of having extra-long CD-Roms (for those curious, that's a Plextor 24x CDRW in there).Installing this optical drive was a pain since the power supply was in the way (this is not a problem in most SFFs since their PSUs are located elsewhere). and there wasn't enough space to plug in the IDE cable. In the end, I did have to remove the PSU, but if you use a CD-Rom under 8 inches deep, there should be no problem leaving the PSU in.
Another improvement made is the 300W power supply. One sticking point from last time was that since we had another bay to use, we would have liked more power. At 300W, Soltek has delivered, and provided the most power among practically any SFF. The 50W power boost gives far more than what 1 bay will use (DVD burners use about 25W), so it gives more headroom for CPU and graphics cards.