As a software developer for many years, I've learned that the best workflow happens when you have lots of screen real estate. Productivity is simply so much higher when you don't have to shuffle windows around and all the relevant information is visible at the same time. So for years, I've dreamed of working on a triple-head system, but didn't have the opportunity to build such a system until recently. Let's just say I'm enjoying it :-).
My next two priorities after the displays were disk and CPU speed. My development requires running a sizable database on my local machine, and I wanted to eliminate hardware bottlenecks as much as possible. Using an SSD in this case was a no-brainer.
The video card was chosen primarily because of the available outputs for driving the displays - this box isn't typically asked to do lots of 3D video.
I opted for a MicroATX tower just to save a little space. The Define Mini is a nice case, but could use some more room beneath the motherboard tray for cable management. Even though I have only a minimum number of components right now, it was still quite a tight fit, and in fact took two people to hold the cables in place and slide the cover back onto the case.
Finally got some pictures added. You can see that most of the case is just empty space. Probably could have gotten something smaller, but reviews for most of the small form-factor cases I looked at indicated that they were pretty hard to work with, being cramped.
You can also see my normal development setup: two side-by-side browser windows on the left monitor, with terminals underneath. In the middle, gVim, where the magic actually happens. And on the right, git-cola, for viewing/staging my current changes, along with gitk, for viewing already committed changes, with more terminals underneath.
When the need arose for multiple VM images, 256GB just wasn't enough, so upgraded the SSD from the Samsung 840 Pro Series 256GB 2.5" SSD.