From this http://www.gamasutra.com/view/feature/6471/the_valve_way_gab... it sounds like their employees shuffle between projects and teams pretty frequently. I imagine some employees are more mobile than others, but from the sounds of most things about that studio, people are rarely locked down spatially unless they want to be.
Those desks are surreal. They have their own built-in power distribution and wiring looms, so all of the cords for monitors, the PC, sound, and so on are bundled out of sight. You only need to unplug one AC cord, trundle the whole thing down the hall, and plug it in when you get where you're going.
