Without this search is not very useful to me at the moment. So I use Google to search HN since they do offer a filter
2. Points filter and comments filter would also be great (> 10 points and/or > 5 comments). I get lot of results which have no activity
I think a good feature to add to HN Search would be some kind of clustering of the same link. So if a link has been reposted many times you can see all the discussions of it in one result.
2. Yes, there is actually a trick in the query syntax: if you use "points>10" you'll get all posts that have more than 10 points. I'll plug the filter on the number of comments as well (like comments>X). Do you think we should rather have sliders?
In your experimental UI, the sidebar can expose all these filters without cluttering up the main UI