>It'd be nice if HN allowed us to collapse entire conversations.

There's a whole bunch of extensions/plugins/userscripts for HN out there, including ones that implement thread hiding. I personally use Hacker News Enhancement Suite for Chrome.

Hey, that's a great idea! Now excuse me while I come up with it independently.

You better trademark/patent/copyright that idea right there before somebody does it and "steal" your precious work :)