I've actually started to use it to teach Javascript to 10 year olds in my local primary school (through a CodeClub I run). It has been a great experience and a lot of kids are moving quickly through the campaign levels. I even have a few kids who moved on to the multiplayer levels.
Quick remark: the computers in the school are Core 2 Duo machines with 1.75GB of RAM. They are running the latest version of Chrome on XP but often crash on CodeCombat (lack of RAM?). It's a shame but reloading usually solves the problem. Also, getting coordinates on the map is usually quite tedious (it doesn't seam to work all the time).
I am really excited about the future of CodeCombat.