One thing I'd change is this error message which is not really an error message : "ERROR: Sorry, that's not correct. Please try again."
It appears every time I try some command which is not exactly the next step defined in the tutorial. It kind of feels like an old school tutor forcing me to follow a rigid book exercise and discouraging experimenting.
If you want me to complete the tutorial, don't move the progress indicator until I complete the next step, but please don't scold me with fake errors :-)
One thing I've been craving for is a place where I can jump in and get a quick primer on some random topic from another programmer. Think SO in real-time. I know there's IRC, but it's not very user friendly and I don't want to hop around different channels to ask different language questions.
If you build a truly social and interactive site for learning programming, I'd use it a lot.
Good luck!