I have joined a couple of new forums lately, and also made one of my own. Pretty much all of them are sound places, but I guess it might be because they are mostly to do with "niche" interests. You'll find that here we get no trolls, because the only people looking for a place like this are people like us: with something constructive and nice to say. Same with the miniature painting forums I have joined, they're all lovely, friendly folk, and even the arguments never even verge on getting rude, they are always civil to each other and respect where each person is coming from.
It's only really popular sites, like YouTube, Myspace etc where you get trolls, because it's easy to do in those places. The more people signed up to a site, the higher chance there is of a few bad eggs in the mix.
Just do what I do when someone makes a negative comment: laugh at how dull their life must be if they are exerting time and effort into leaving cr@ppy comments about people. It's obvious they are pube-less, socially deficient jizz-dispensers, so why waste the energy on fretting? :D