While it might not be a major pastime for me, I enjoy learning about magic. Not of the satanic ritual variety, but of the slight of hand, stage/street variety. Sometimes I like to use this to harass my friends with impossible tricks, other times I just do it to practice some fine technical skills. In this case, namely how to throw playing cards.
If you have a deck, go grab it right now, and try to throw a card. Watch, as it flops to the ground like a piece of paper. Now, grab it by the corner, and try throwing it like a frisbee. Suddenly, the card will move in a straight line or arc, and, depending on what you're throwing it at, lodge itself in its target. Why does this change in motion change the outcome of the throw? To explain it simply, by spinning the card, the angular momentum of the card prevents it from being easily rotated in another direction. Combine it with the low air resistance that you create on the card's edge when throwing it in such a manner, and the air resistance prevents the card from actually fluttering down like it would if not spinning.
While I'm on the topic, let me mention that, while it could stick in the right target, a playing card CANNOT be used as a weapon. Due to its relatively low mass, it would lack the sufficient energy necessary to cause more than a small paper cut to the human body. If you don't want to believe me, however, know that this myth was tested by the MythBusters, and a card launched at 150 mph by a machine didn't have enough energy to cause more than said paper cut.