You'll be fine. If you like programming and it sounds like Hacker School would be fun, you should apply. The minimum experience you need to have a good time and learn a lot is very low, and if you're writing a book on Clojure web dev then I'd bet you're way past it.
Disclaimer: the book is written under the pretense of "by a beginner, for a beginner", so it isn't exactly the best material ever, but I feel I'm getting good coverage on the main topics. I'm currently pushing hard for people to peer review the initial chapters before I continue into the next bulk of it so I can make sure the style its being done in is conducive to learning the material effectively. I don't want to plug it here because I'll seem like a shill, but if you are interested I can share the link privately.
Source: I'm a current Hacker School student