The twcenter.net has a better community when it comes to manners, to name just one example.
It does seem pretty mature for the internet, but I've still seen many whines and such on there too. I think that type of game attracts a generally more mature dedicated player. Also, it's a decently small community, so there's less mob mentality.
I've been a long time TeamLiquid(big sc2 forum) lurker, and while it was never the pinnacle of maturity, since its member base has exploded with sc2 the average maturity level has plummeted.