Thanks! Believe it or not about 70% of the revenue comes from the Creating Effective User Stories course. I have another course in the same vein, Agile in the Real World, coming out in a few weeks that I hope will do as well.

The trick seems to be to find a niche that people are interested in and that will continue to be interested in for some time, since the course revenue will decay over time.

For me, agile seemed to be that niche...groovy, not so much :)

It also helps if you already have a brand going in. For example, if you're already well known from books or a popular blog you'll have name recognition and some of your audience will follow you. This wasn't the case with me, but I've seen it happen several times with more well known authors.