I agree with you on the Carvin forum, and I'll risk mentioning the Peavey forum here as well. While both of these brands take a lot of abuse from some folks because they make a lot of low-end stuff (especially Peavey), they've both produced some very respectable products and earned loyal followings over many years.
Both forums will have more boneheads (again, especially Peavey) than the Mesa forum, due to their positions in the marketplace, but they also both have their share of very intelligent gear wizards and accomplished musicians.