SFF PC's have been hitting the market hard lately. Shuttle started it all off, however Mini-ITX seems to be picking up momentum, and may allow for a more robust and upgradable route (Since ITX merely a standard like ATX whereas shuttle redesigns motherboard for their cases). Planet Savage has a nice review on Lianli's Mini-itx case that you guys might want to check out.

"The advantages of Mini-ITX are easily apparent. Not only does it lets you save space but also provides for a quieter working environment. This form factor is perfect for office and home PCs alike and is surely the image of computer desktops in the future. Skeptical? Think of this: at one point, performance will plateau enough to allow for smaller devices to do what larger units do. Look at current laptops for example. Mobile GPUs such as the Mobility Radeon provide for solutions for gaming needs. It won’t be long before we could do even more with less."