[discussedbefore]

I use HN search all the time; it's useful.

There is no way to search across multiple comments on the same "story"; I use Google site search for this.

It only counts replies/"comments" for stories, not comments (which would probably be a lot more work).

It differentiates between plural and singular search terms as very different searches.

The only ranking options are by popularity and date (would like to be able to sort results by number of replies too).