Just checked out the Mumsnet gt forum - what a yawn. If I want the sanctimonious comments spouted there, I can just talk to anyone in real life. Nothing useful at all, certainly nothing like the extreme wealth of knowledge, experience and nuanced commentary I have read here.
I enjoy MDC for the AP angle that is prevalent - if there are people who have squared the circle how you can "let a child be a child" and "follow their lead" while still meeting their academic needs that is where they hang out.