I did a presentation on motivation and procrastination research to the Seattle meetup group and an exercise trying to apply the material to a real life example. Eight people came. They were a skeptical bunch and questioned me on exactly the parts I am most interested in an know the least about: how exactly scientists assess the psychological quantities (expectancy, value, delay and impulsiveness). I'd like to learn more about the research and be able to give such presentations to others in the future. I'd also like to record a presentation like it and put it up on the internet.

People seemed to think the exercise was pretty valuable. It was also fairly fun. The presentation is here, the exercise is here and here.

Luke's suggestion for how to learn how psychologists assess expectancy, value and delay was

As for how scientists assess the relevant psychological qualities, and for why the 'procrastination equation' is taken seriously, all the references are provided in my post 'How to Beat Procrastination'. I also uploaded quite a few of the studies myself so anyone who is actually interested can check the data for themselves. (Prediction: Almost nobody will.) 
The papers in footnote 6 are the place to start, for they explain why the equation (called temporal motivation theory by researchers) was developed to predict experimental results, and those papers point to all the individual studies which show how scientists assess expectancy, value, delay, and impulsiveness. For example, 'expectancy' in TMT is measured under a variety of psychological constructs, but largely by measures of self-efficacy and optimism.
There is no short summary of these issues, though Piers Steel's recent book 'The Procrastination Equation' is a decent attempt while being much longer than my article. Psychology is very complicated, and our understanding of it is less certain than our understanding of physics or computer science.