This was my experience too. I found that I was productive 2 hours each day. The time tracker helped bring this up to 4 hours in an 8 hour day. I would play a game where I would try and beat yesterdays score.

Unless you have your own office, or at home or coworkers are forbidden to talk to you on pain of death and torture, I find it extremely difficult to be more productive than 4-4.5 hours in a 7-8 hour block of office time.