With forums you often get a topic that has 500 posts, 480 of which are pure "me too / works for me" noise. Those 500 posts are split into 50 pages of 10 posts each, and page one has the oldest posts. The post with the answer is on page 46 and the pages after that are just 30-40 comments thanking whoever came up with the answer. So if you jump straight to the end then start working backwards, you're looking at maybe 10 or so page loads before you actually find the answer you're looking for.

Some forums aren't shit, but all of those cookie cutter PHP forums all seem to be shit.

QA forums are trash and they were totally replaced by stack exchange but general talk forums are still quite good. Private torrent trackers always have forums attached and the quality is usually quite good because its very hard to get a new account if you get banned.

From what I have seen, private forums are much more civil but its tough to actually build a community when its so much effort to join.

This is exactly why HN/Reddit format of tree-structured discussions is superior to linear phpBB forums. They allow for segregating subtopics (on a long forum thread, there are always subtopics and offtopics), letting you ignore the things that are not relevant to you.

Were I setting up a discussion forum today, I'd immediately look for something halfway between HN and Reddit. Reddit itself is too much of a PITA to host (we tried in our Hackerspace, but didn't go too far); HN has too little markup and no built-in functionality for storing notifications about replies.

lobste.rs has open source base IIRC and has notifications built in, at least in the public instance.

And a fair number of those thanks and me too posts are actually SEO spam with a profile link to some other unrelated site...

IRC deep conversations do happen and indeed you want persistence for those. Communities which rely on IRC use IRC logs for that. Perl projects use IRC that way and I think the Mozilla guys too.