Nice work Peter. I wrapped this in two lines of Sinatra and deployed it to Heroku, so anyone can get an RSS feed for their username:
http://hackernews.heroku.com/username
Code is here: http://github.com/jnl/hackernews-thread-rss
Code is here: http://github.com/jnl/hackernews-thread-rss
Out of curiosity (and in hopes of eliciting a reply to see if it shows up in my new Hacker News Responses feed!) would this also be easy to do with Yahoo!Pipes?