I asked that same question when I first joined the forum. I was directed towards the recreational and family forum and the general cycling discussion forum.
Since I have a hybrid and I'm looking to get into some serious riding, I do my posts in the road cycling forum.
If folks are posting their comfort bike questions and comments in the mountain biking forum, could you report the posts/threads so we can move the post/thread to the correct forum? Personally, I do not ride a mountain bike, so I really do not spend a lot of time in that forum policing it. I more depend on the other mods like A2, who seems to get into the mountain biking a bit more. It would be a relief if the mtb folks could help out the mods and let us know when it's happening. We can move the posts and send a PM to the member so they do not continue to interrupt the flow of the mtb forum.