I've recently started learning to play the guitar using this site, and it's amazing. The instructors' style is entertaining (contrary to the guitar course I bought on dvd, which is only useful if I can't fall asleep at night - 5 minutes of that stuff does the trick), the lessons move at a pace that's just right, and I'm happy with the progress I've made in just two weeks.
One thing that would make the materials even more useful for me is if I could download a course for offline viewing on my iPhone (which doesn't play flash videos) and thus could be learning new stuff even when I don't have internet access (holidays, business trips, etc.). I tried out downloading a flash-video, recoding it to an iPhone-compatible format with handbrake (http://handbrake.fr) and transferring it to the iPhone, and it worked just fine. But doing that for a whole course takes a lot of preparation time (waiting for the downloads, converting each clip individually, ...).
Is this something you would consider providing on the guitartricks website directly? I'm thinking of "download this course for offline-viewing in format XYZ"-buttons on a course's starting page. (XYZ being a selection of common video formats).
I don't know if anybody else would be interested in this, but for me it would make guitartricks even more usable, and available all the time.