There has been a flurry of activity on the internet discussing a huge difference between the productivity of the best programmers versus the productivity of the worst. Here's a typical Google result when researching this topic: http://www.devtopics.com/programmer-productivity-the-tenfinity-factor/

I've been wondering if there has been any research or serious discussion about differences in day-to-day productivity by the same programmer.

I think that personally, there is a huge variance in how much I can get done on a day by day basis, so I was wondering if anyone else feels the same way or has done any research.