I like this a lot, and think it's the best intro to Rust yet. The thing that concerns me a bit is that it presents the special cases in concurrency without impressing some of the most important points. Primarily, the channel example presents the send as copying, which in this case it is, but one of the main advantages of Rust's channels and owned types is that message passing of heap-allocated types do not need to copy. It probably doesn't stress hard enough that Rust tasks do not share memory before saying, 'oh, but really you can share memory if you need to', though I see that the Arc and RWArc examples are good ways to introduce the concept of using unsafe code to provide safe abstractions.