Ever tried to organize a surprise birthday for a friend? Well, the huge problem about surprise birthday parties is that they never actually come as a surprise - people KNOW when they have birthday, so if someone takes you to a surprise place on your birthday, it isn't very hard to guess what's gonna happen.
Introduce the REAL surprise birthday. Let the government give everyone a random surprise birthday that changes on a yearly basis. Make the info available to everyone except the person celebrating his/her birthday. Will solve other problems, too, e.g. people heading for a round birthday won't have time for a midlife crisis. Also, people whose birthday used to be in December will get a fair chance to celebrate it when it's nice and warm.
Reward: Throw a surprise birthday party for me.