We (the Eclipse platform team) added a dark theme contributed by Andrea Guarinoni to Eclipse Luna M6. Lots of people were asking for a default dark theme. Of course SWT CSS styling has some limitation but were are planning to work on these. Having a default dark theme will help us doing so, as more people will start using it and might contribute to it via bug reports or patches.
Here is the Eclipse IDE using the dark theme under Linux.
And here is an RCP demo application called contacts which imports and extends the dark theme.
As you may noticed some of the icons are still looking ugly. We received another contribution from Tony McCrary from l33tlabs.com with a new set of icons for the platform and we are in the process of integrating them. For the platform ui icons, e.g., save and the like, we should be done already and I created Gerrit reviews for other platform components, like JDT, Debug and PDE and hope they pick them up soon.
If you want to test the new theme, go to http://download.eclipse.org/eclipse/downloads/ and download the M6 milestone. We are already working on some improvements for M7.