About a year ago, Carl and I were doing a training in Washington DC. When we got to teaching Drupal themes to a bunch of qualified people with HTML, CSS and some PHP knowledge, we listened to our own explanations, looked at each other, and both thought "it shouldn't have to be this complicated!" Drupal 6 theme development was different than Drupal 5, and Drupal themes in general were still a beast unlike anything else, but with a little explanation, people got it, and people learned to appreciate Drupal 6 theme development rather quickly.
There are a lot of great things about being a Drupal Trainer. My favorite is getting to see -- first hand -- how the code we write affects the community.
I noticed that with the release of Drupal 7 - the demand for training on theme development increased dramatically. It took me a while to figure out why - exactly - but after a night of heated Debate in IRC with chx, mikey_p, HedgeMage, heyrocker, and yoroy (among others) we may have arrived at a conclusion.