How I Use It
I used learn.code.org during the nationwide, "Hour of Code." I initially meant to spend one 40 minute class period, but ended up spending several days. Almost all of my students completed the Hour of Code tutorial. I needed a better bridge between learn.code.org and Scratch. I will most certainly repeat the Hour of Code next year.
So far as to introduce coding to my students each year during the "Hour of Code," there's nothing better. They didn't realize they were working and using their brains for computational math. There are a few tweaks I would make to the system, and if you're teaching in depth code, you'll need more.