I don't think there is anything wrong with some useless random babble threads, but anything in excess, especially from the same poster, becomes irritating and annoying to the rest of a forum population that aren't interested.
It's part of the unwritten rules of internet etiquette.
Posting every random thought that comes to mind in a professional business forum is not proper forum etiquette, that's what myspace and the like are for.
This is no joke, this issue has come up in every single message board forum that I've ever been a member or lurked in. I've come to the realization that it comes with the territory and I'm willing to deal with it in trade for all the useful info I get out of them.
What I have seen work in other forums are what I call "chat threads". It's a thread where a group of people (friends) can spam a way all they want. This way it only occupies one spot in the "new posts" section. Another option is to create a discussion group, where people can just shoot the crap in.
I do admit I get annoyed and irritated sometimes, but nothing that I can't deal with. Just my two cents.
Carry on....