Still, though, this feature really should be part of HN proper, especially since it's so simple to implement. I think a lot more attention would hit posts that aren't already at the top, which would encourage people to write new posts instead of responding to whatever happens to be above the fold.
It's not going to fix the comment quality problems, but it would give a bump in the direction of wider, shallower comment trees, which will probably help a bit (deeply nested comments tend to either meander off topic or degenerate into arguments between a couple of people).
http://alexander.kirk.at/2010/02/16/collapsible-threads-for-...