Sounds interesting. Do you mind sharing how did you trained your machine learning algorithm ? It seems like an awfully hard task, since in a sense you are competing with the Google algorithm and the order it offered you.
The reddit search engine isn't very good. It's just logistic regression with a number of features, like the percent of 1, 2, and 3-gram matches, it's score, number of comments, and if it's a selfpost.