Once I did, I could continue with the lessons, quit with I got tired/bored (my work was saved automatically), and then sign in later to continue with my saved work. On signing in, you are shown a summary of the lessons you've completed and which ones you have yet to start. After you successfully finish so many lessons, you "earn" achievement badges. For making it through the first four of eight lessons, I earned two achievements.
The lessons are fun, easy, but inflexible. If you deviate from the lesson in the slightest way, you will get an error message. While a hint is provided with different steps in each lesson, if you get stuck, you don't get any other help except to offer feedback about the lesson. There's no way to just get the full solution presented to you. That's good on the one hand, because you aren't tempted to give up too easily and it "forces" you to try and figure out what went wrong. On the other hand, it you truly get stuck...you're stuck. Lessons build on one another (which is a good idea) so if you can't figure one part of a lesson out, you won't be able to just skip it and move on.
The scope of the course, "Getting Started with Programming", only spans eight lessons, ending after the lesson on "while loops". There's no obvious way for me to tell after lesson eight if I'll be able to continue with what I've started to learn. I clicked the "Courses" link in the header menu expecting to see extended (possibly for pay) courses, but all that appeared was the eight lessons for the basic course.
Once you log out, you're returned to the start page. The other options on that page include subscribing to an email newsletter, and sharing your experience with your lessons on twitter and Facebook. Presumably, this is part of how Codecademy plans to market itself. Oh, there is a section called "Create a Lesson", so the Codecademy folks are interested in external participation in expanding their project.
Codecademy seems like it's a project in the making. Since they harvest your email address, both as a condition of creating an account, and during the pre-account lesson when you're asked to enter your email address, I expect that once Codecademy has a sufficient database of names, they'll advance to the next phase of whatever their plan happens to be. That could either mean further lessons will be for a fee or they may continue to offer more advanced lessons without charging.
I'm hardly the first blogger to post a review. About two weeks ago, TechCrunch published their write up on Codecademy, including a talking to Codecademy co-founders Zach Sims and Ryan Bubinski. Sims commented several times on the TechCrunch blog including, "Hi everyone - we might be a little slow right now but we're working on getting things faster. Thanks so much!"
Other thoughts: The "subtitle" of the course "Getting Started with Programming" is "Time to become a coding ninja". That sounds as if Codecademy's intent is to encourage its students to become proficient and even expert at coding. Three things will have to happen. The first one is obvious. They'll need more lessons. A lot more lessons.
The next two points I take from my own experience. You can't really learn something unless you do it all the time. People don't learn to read and write when they do it only occasionally. They need to practice reading and writing all of the time until it becomes second nature. Even if you teach someone the basics of programming, if they don't have any way to apply it on a frequent basis, they'll lose those skills again. Building in some form of continual practice with periodic refreshers of material covered previously will help.
Finally, students will eventually have to learn to "build" something practical. Learning how to determine the length of a string is fine and dandy, but so what? How does that figure into writing a program that actually does something? Lessons will eventually have to lead to practical projects so that at some point, the students will be able to program independently.
Presently, although Codecademy has gotten a lot more attention than they expected in the short amount of time they've been online, I'm sure they'd love more. If you know little or nothing about programming but would like to learn in an interactive environment, go to Codecademy.com and try it out.