MumsNet is just a website, with loads of different things for Mums/Dad's of children of all ages. Things like afterschool clubs, toddler groups, childminders, etc etc. They also have meet ups, in local places. I've always found it really helpful, so have no idea why someone would class it as "scary". Odd.
I can only recount what I encountered. Not being a Mum I really have no place there, nor do I have a place in the middle-class suburbia that seems to dominate Mumsnet.