That happens too with threaded discussions, it just happens in a many-headed hydra way where the same things are rehashed in 5 different locations that you may not see…
Which is kind of my “sweeping it under the rug” feeling in general with threads. Speaking of rehashing everything over and over, not that I want that to spawn another threaded vs flat discussion… 
I prefer problems out in the open, in a common location where everyone can see and discuss 'em.
Like we’re doing right now!
Over time I am becoming a big believer in the “say your piece and let others talk” strategy, but remember that what we show now is a reminder to pause and let others speak when you post a lot, it is not mandatory. However… I have noticed that some, uh, axe-grindy new users can be problematic and we just instituted a setting that limits new users from replying too much to the same topic. You can read the rationale for that here, and I highly recommend that you do if you have any interest at all in the topic:
http://meta.discourse.org/t/why-is-there-a-topic-reply-limit-for-new-users/11513/2?u=codinghorror
Of course @beschizza is free to set this to whatever he likes including 999. Or, y’know, 666.
BBS users are reasonably good at flagging spam (and thank you for this, keep flagging evil spam for great justice) but yeah, flagging digressions and monopolization is basically not happening at all. There’s a pretty good overall BBS culture now, but a culture of flagging mean-spirited stuff… that seems much harder to achieve.
One thing that I have found works well is for moderators to actually post “hey guys, stay on topic” or “remember, keep it civil (link to faq)” as @Falcor has done. Posts magically disappearing doesn’t necessarily teach the community, but moderators taking a brief, friendly (and I cannot emphasize enough the friendly bit) public stand does.
So I think more moderation is definitely in order – specifically, more of the latter type to complement the former.
