As it stands, I only see codeacademy being useful for programmers who are new to Javascript. If you're completely new to programming, there are too many problems, like the article mentions, that are difficult to get past without knowing... programming!
Even then it is frustrating. I know basic to medium level Java and Python. I wanted to learn Javascript and decided to take codeacademy for a spin. The experience was so frustrating, I gave up after the first few exercises (after shouting at my computer a few times). There was no useful feedback - just an error message like 'Oops. Try again'.
I prefer Zed Shaw's style of teaching. Guess, I will wait until he publishes LearnJavaScriptTheHardWay.
