I really like the simple UX, although I believe others have already provided some good suggestions for improvement.
I'm among the group of visitors who wants to know more before I click any of the big 3 icons. I'm also interested in improving (and adding to) my novice HTML/CSS skills, so I immediately saw value after reading the home page. It came as quite a shock you wanted $50/month to access your full content!
You may want to take this chance to consider a different $ model. Sure, you have plenty of competition- including big name universities- charging way more for effectively the same training. But free substitutes abound. The internet is flooded with tutorials, etc. about how to make stuff for the internet. No matter how much "better" quality you provide, I think prospects will balk at your rates and turn to free resources instead.
But you might still make a lot of money from providing your content "for free". If you only granted access to registered subscribers, you have a great tool for building a strong email list. The demographic has already identified itself: these are people interested in learning more about web & iOS development. There's a lot of cash to be had marketing software tools, templates and all sorts of tertiary materials to this same demo. Imagine the affiliate commission on 1 copy of Adobe CS5.
Also, I found it annoying the "Sign your team up" button on the http://teamtreehouse.com/groups page simply looped back to the main 'Plans' page. Seemed like a mistake when I first clicked; only realized it was intentional after scouring the Plans page to find out "you can easily add other users at a discount". But what are the multi-seat rates?