It depends on what I'm doing.
If I'm doing creative stuff the lights are always on full. I've got overhead lights, plus two lamps on my desk pointed at the ceiling for more diffuse lighting. I even bought a smoked glass table-top to spread the light out a bit more.
I can't think in the dark, I need stimulation. It may hamper my auditory sensitivity, but I feel like my brain is better able to move around the space. I guess a good analogy for how I feel about trying to be creative in a dark room is that it would be like trying to put together a big puzzle on a small table. All of your pieces have to stay in the bottom of the box, because there's nowhere else to put them. Creativity needs a lot of room to spread itself out.
Also, it's harder to stare off into the distance when you can't see anything.
On the other hand, when I'm doing more precision stuff, mixing/EQing/level matching I tend to keep it darker. Not for the specific reason that your (seemingly slightly mean) former boss used to give, but just because it feels better that way. Come to think of it, I guess it does kind of force the focus onto the screen and what's coming out of the speakers...
My interest of late has been moreso in the creative side of things than the technical, so the lights are up full most of the time.