Completely agree, it is rubbish. They just want your personal information - I know that's the point of all loyalty cards but this doesn't offer a reasonable reward in return for that info - An M&S employee even agreed with me the other day when she asked if I had a Sparks card as she served me and I told her I don't bother with it any more.
Hope you're reading this M&S, you're really p'ing your customers off by treating us like idiots, do you really think wewe're that gullible?