In the inflexible environment, surfing net locations that were somewhat work related was the only thing I could do to pass by time when I knew I wasn't going to write quality code or when I was too mentally tired to accomplish the task that was at hand. I had many times where going home and returning in the morning was the best thing for trying to solve a difficult problem.
Unfortunately, many employers don't care and want to fit development staff into the typical 9-5 mold even if it means reduced productivity.