I absolutely love the dark interface. It was one of the primary the reasons I updated.
It makes the photos look like they are in a dark matt, which to my mind, is the best way to present photographs, most of the time. Some look better in a white matt of course.
When runnning PM on one screen and LR on another (for example) they sit in really well with each other. It just LOOKS professional.
Having said all that, I can understand that on smaller screens and in hard light reflecting off a monitor, it would be a bit impractical. The ability to change that in the preferences is a good move to keep every one happy and as your environment changes or moving from desktop to laptop.