I seem to spend a lot of time poking around trying to figure out what you have. The nice thing is that I keep discovering more lessons I'm excited to get to learn. There is a lot to learn on this site.
Also I'd like to suggest that there be links to songs and/or other exercises that would enhance a particular lesson/level to make it more interesting and provide more practice material for a particular level especially for the chord changing lessons. That's when I find myself navigating through the rest of your site when I get bored practicing the same exercise but not yet ready to move on.
I've also noticed that not all the songs you teach are in your song list. It would be nice to be able to quickly access even the simple lesson songs.