Swift is now open to anyone to try out, just a free registration required to download XCode 6 beta: https://developer.apple.com/swift/

I've made progress through the ebook and running the examples side by side in a playground. It's been a great way to learn not only the language, but also filling in some knowledge gaps I have.

Closures is where I'm running into some issues understanding their purpose, and difficulty performing the experiments suggested in the book. I think building a few actual things will help my understanding though. As XCode 6 is stabilizing, I'm getting closer to starting work on an app.