I can't believe 'yummy' has changed it's meaning. I think 'yummy mummy' is a compound noun. In fact thinking about it it's mummy that has always been laced with all the class baggage. I grew up calling my dear one, 'Mum'. Best YM/MILF ever had to be that advert where the lad watches his mates mums assured hand movements as she prepares their breakfast while correcting a pleat in her skirt, and puts a shoe on, and once she's gone he says "Sean, I fancy your mum" and then the advert finishes in silence. Genius. Mind you must be rubbish as advertising as I couldn't tell you if it was for shoes, breakfast cereal, fairy liquid or Crystal Clear face cream.