Before I did hacker school, I thought I was a good programmer. But being in a room with 20 incredibly smart people really makes you realize what you don't know. Since joining, I've:
-Authored a (now-committed) patch to the python core
-Written a SPDY implementation
-Contributed to many open source projects
-Learned C and Rust
I've also made friends that I hope to keep around for a long time.In short: If you have any interest, even if you've only done a bit of programming before, apply. They select on passion for self improvement, not skill.