I've done it for various lengths of time, depending where I was at and how busy we were. Some times I could be on and off all day, sometimes just on lunch, or a few minutes here and there.
Where I'm at now what I'm doing, I don't at all, I wait until i get back to my hotel.
Very busy on a project and desk not set up to be surfing without being noticed too much. Maybe when we get the project through this "hot" phase, I can do a few minutes here and there.