I like dark colors. People that know me are used to see me usually wearing dark clothing.
I usually have a solid black, unthemed background on my empty Windows desktop. I might put some wallpaper for a while, but they are always dark and not too distracting.
I have dark themes on some of my machines OS, at least as much as Microsoft lets me (less in each new version of Windows).
But one thing that since around 4 or 5 years I've been doing is changing my IDE source code color scheme so that it uses a dark one.
1) To code at night
I am a creature of the night. I have problems if I want to go to sleep early because my brain still wants more action, so quite a few nights I stay until late, with dim or no light at all, coding a bit. If I leave the typical default white background, I can get blind in no time, and I already wear glasses so I don't want to make things worse.
A dark color schema helps me work at night without hurting my sight.
2) To focus on what is important when viewing code
Small example; Take a look at this code fragment:
Do you get distracted by the comment block at the beginning of the method, or did you focused first on the definition and the code?
I like color schemas that put comments in dark colors so I don't get distracted while reading code. Commenting is important, but if comments are in bright colors they tend to distract you a lot, and what really speaks about the code it's the code itself (or else you should refactor your code).
Strings are in a different color, generics parameters are in grey, but in general the color is just blue and lightgrey, helping me read what is important and leaving the comments "in background" for when I need to take a look at them.
My eyes and my brain gets used to this low amount of different colors for different meanings, and takes less time to process.
Vim is dark by default. Sublime Text is dark too. Visual Studio 2012 comes with a dark theme now. So this looks that is not just a hipster trend of "let's use dark themes to be different", it can actually help you focus on coding better. Or at least is what I like to think...
Bonus: This are the two sources I use for my IDEs. If you have more feel free to leave me a comment pointing to them.