Originally I had been turned on to the VS Theming trend by Scott Hanselman’s post about theming Visual Studio.
When I went back to his blog to get the link for his post, I saw that it has been updated and now there is an entire site dedicated to Visual Studio themes:
There are a ton of great themes on this site, and you can even make your own.
For the most part theming your environment is just a fun way to beak up the monotony of an application that you spend WAY too much time with. But, I have also found that after switching to a darker theme that I have reduced the amount of eye strain and fatigue associated with marathon coding sessions.