Although I also do pick up books myself because of awards, my main source of "because it won an award" books is my mother's frantic Christmas buying. If it has AWARD stickered on its front, there is a reasonable likelihood I will be given it as a gift.

Which has introduced me to, e.g., Colm Toibin, whom I otherwise would never have heard of, so I can't complain overmuch. Probably her tactics are what introduced me to, e.g., actually writing down what won the Tiptree every year, and eventually tracking down a copy.