I dont even expect an actual campaign but if MNHQ could just refuse adverts or reviews of products that are aimed solely at girls or boys then that would be a start.
Up until around 9 yo there are no significant anatomical differences between girls and boys that should influence clothing or toys. I have no objection to pink baby grows or fairytale castles but if you market them explicitly as 'for girls' then I do have a problem with it. Let people/kids make their own minds up.
ps. the Boys Future Star T-Shirt advertised on the www.mumsnet.com/christmas/top-childrens-christmas-presents-2011 page is now a 'kids' T-shirt as I contacted the sellers about it. If you could amend the link that would be lovely!