Calibanbutcher said:
ONE thread on a topic at any given time is enough. If you have something new to add add it to the thread itself.
Define "any given time" first.
Yes, it gets silly when there's half a dozen almost identical threads on the first page of the forum, but I'd say once it's off the first page it's fair game for a new thread from the casual forum visitor, and by the third page it's fair game for the rest of us.
As to adding to long existing threads - personally once a thread hits 5+ pages of replies at most I'm very unlikely to look at it again unless it's a thread I started, and/or I get a reply notification in my inbox when someone quotes me. I'm sure that's true of lots of forum goers. So any comments tagged onto the end of a long thread are much more likely to go unread by most people, especially if they're only peripheral to the original thread topic.
Finally, what is or isn't on the 'same' topic? I started a thread today wondering why
The Empire Strikes Back is more popular with fans than the original
Star Wars. Does that belong on other recent Star Wars related threads? No, because although it's Star Wars related, it's got nothing to do with Episode 7, JJ Abrams or lens flare.