I'm very new to geocaching, but it looks like the idea of leaving business cards in a cache isn't original. Neither is the fact that some people will just trash your ideas for the sake of being mean.
Most of the cache's I've found so far or read about in my area are ammo cans or "tupperware" boxes, size varies, and most are filled with stuff from people's junk drawers, lots of toys and other fluff.
True finds for me aside from interesting locations are unique coins/tb's with some sort of purpose and individuality for the person that first left them. As such I don't see a problem with people making up nice, personal "Cache Cards", laminating them and even getting tracking codes for them and sending them off like all the others. Makes more sense than a ratty beanie baby with dog tags to me, but to each their own.
Laminated business cards take up very little space in a small container, they're weather proof, and they are cheap, personal, trackable, and even collectable if a creative person makes a series of them and sends them out.
I love the idea of coins/medallions/tokens, but face it, the urge to keep and collect them is strong and many are lost because of this.
I would be against using cards as a lazy way of logging your visit, especially when stapled to a logbook, but what's the problem with using them as I've just stated?