I'm a girl, so I can't answer from a guys point of view - but I think it's pretty obvious why a guy likes them, they make legs look absolutely amazing. It also gives the kind of element of half wearing clothes still and being that caught up in the moment. There's something quite sexy, to me, about still wearing clothes because it seems to highlight just how naked you are.
They have amazing stockings in La senza, by the way, and I think they have them on a 3 for 2 deal. My suspender belt is from Ann Summers though, think it was around €12, you just clip the suspenders (attached to the belt), onto the stockings.