I wouldn't discount the idea of a gay, black, or left handed Ubuntu user forums. I know four other Linux users in real life and they are all in my Transgender support group. I've wondered more than once if I should start a Trans-friendly forum.:P
I see two possible values to having a sub-forum for a specific group. The first is if the group has a perspective that is different from the mainstream and might have insights that can benefit Ubuntu as a whole. The second is if they use their computers in a different way, or use different sorts of programs.
Gender differences are often subtle and it can be easy to discount them but they are there. Small differences in the ratio of gray matter and white matter in the brain gives men a tendency towards linear logic and women a tendency towards associative logic. Cultural conditioning often reinforces these tendencies.
Programming logic is very linear and maybe this is why computers have been traditionally a more male field. However what makes computers important is the way they connect to each other, and allow us to connect. That's a more associative process.
So I think it's possible that women do view their computers in a slightly different way than the average man. Whether I am writing, sharing photos with friends, using social media or surfing the internet my computer is a platform for communication. Do other women feel that way too? I don't know. Does this give Ubuntu's development team some great new insight or innovation? I don't know that either, but I do think it's worth discussing these questions.
Sorry for the long post. I am Rachel and I use Ubuntu.):P