Personally I don't feel like its just everyone's business.... once you get to know people, and if you be yourself, then they will probably have an idea. If it is a guy or a girl you are going to get into a relationship with, then I think they probably have a right to know before becoming committed to you--especially if you think that means its okay to "chet with whatever sex you are not in the relationship with. If you are dating a boy... then its okay to see other women... or if you are with girl... then boys don't count, etc.
You should really be very honest with yourself and question your motives for telling others. Think about who you want to tell and why. Is it a coworker with no relationship to your family? Or is it a family member who would be shocked with the news? Many try to shock others in order to get attention. Many try to do it to show the other people do not understand them as well as they think they do. There can be deeper issues which go well beyond sexuality. Victims of abuse can also struggle with relationships and identity. If a woman is abused by a man, they may seek out other woman for love. If a man is abused by a man, he may think it's because he was born gay. Often times the physical abuse can be confused with real love especially if the abuse is coming from a parent or family member. Consider your rational for several weeks. Think about it, Pray about it. Mediate on it. What truly do you hope to accomplish? If you have been in a loving relationship for years and starting showing up to all the holiday meals with your best friend, most family members after a few holidays are intelligent enough to figure out he or she is more than a roommate. This slow acknowledgement can be easier for people to deal with. It's easier for mom or dad to realize they may not have the traditional grandkids they hoped for.