I've liberated myself from any reward card and it's a great pleasure. I did have one great moment where I paid for a huge pile of Christmas presents with the points proceeds of Dh's daily meal deal at Boots, but it's frightening to think about how much that moment cost.
For me, M&S USP should be their customer service, that's what it always used to be and that's what they should focus on. Once upon a time it was about the only big shop where you got treated like a valued person - where did that go? The managers could be on the shopfloor for at least 2 hours every working day helping people to find what they want, refining the layout, range, stocking, buying and service and earwigging on customer conversations.
Instead they appear to have designed their loyalty card scheme from the starting point of 'how can we flog more womenswear' as opposed to 'how do we get our customers feeling like they want to come back' which is surely the point of a loyalty card.