For me, productivity changes on a day by day basis. There are days when I'm able to stay focused and work from 8am to midnight, taking a half-hour lunch break and a 5 minute break every 3 hours and I actually get a lot done in that time. On other days I work for hours on end on the same thing and won't get it done because I keep procrastinating, checking HN, reddit, whatever.

I think it's a lot about being motivated and excited about what you do. If it feels really interesting, the work is basically doing itself. If I've got other things on my mind (which I have lately), everything feels like a chore. Still have to do it though. The same even applies to my personal projects to a lesser degree.