I think the requirement of account creation is a hinderance to helping spread the word of the site...I don't really have any intention of following these lessons (because I've used Foundation before and know CSS pretty well) but I would recommend them if, after skimming them, the site's implementation is well done.

I understand the desire to gauge user interest and get their contact info, but why not let the signup process be more organic (i.e. you sign up after the first few lessons because you recognize the value of the service), as it is for Codecademy?

(there is a "view lessons" in the top right, but it's not intuitive, given the signup modal)