Thanks for your answers. I think that the 'cons' have it. Along with mothers day, fathers, day etc., all invented by WH Smiths or Woolworths if you ask me.
Mothering Sunday is actually a Christian celebration so even if it is exploited by card companies it wasn't invented by them! Anyway it's nice to show your parents you care!
Actually, seeing as its actually "St" Valentines I presume that is actually a Christian thing