I thought it was useful when pregnant and when DCs were babies for articles etc. I used it to find my local Tamba mums groups which was fantastic in the early days. The discount is great for some places. I used it mostly for Clarks shoes.
I'm not a member now though - magazine is pitched at parents with babies and toddlers and mine are school age. I use MN for advice on older DCs.
They also do member's only parents courses which have good reviews. Message boards are good. I joined because I want to be a part of our membership organisation i.e. support their research into twins, ante-natal guide etc. All the things which might help parents etc in the future (and for the jojo discount..!)