The howto refreshing to read. While I love JS as a language, even written longhand, it feels like you've brought an uncommon elegance to it. The syntax is much simpler and maps more cleanly to how I think. It feels a lot like Ruby.
Granted, most of the JS I work on is in pretty complex applications, so I'd be hesitant to work in anything but the target language itself. But it's a very clean abstraction or concept to begin with. I'd love to see something complex written in CoffeeScript, especially with DOM manipulation or another JS framework involved.
It'd be fun to try writing a DSL or simple compiler sometime. This must have been very interesting to create. Cheers for such detailed examples in the unveiling as well.
Great job, and thanks again!
Edit: Hahaha, thanks for the examples from the Poignant Guide. Pouring out a few drops for _why right now.
Edit 2: Forgot that you wrote underscore.js - thanks for that as well. Crazy to see how simple it is when written in CS.