From the FAQ: Geni is a unique approach to solving the problem of genealogy, which is the question of how everyone is related. Geni lets you create a family tree through our fun simple interface. When you add a relative's email address, he or she will be invited to join your tree. That relative can then add other relatives, and so on. Your tree will continue to grow as relatives invite other relatives. Each family member has a profile which can be viewed by clicking their name in the tree. This helps family members learn more about each other and stay in touch. Family members can also share information and work together to build profiles for common ancestors. Geni is a private network. Only the people in your tree can see your tree and your profile. Geni will not share your personal information with third parties.
See also, my previous post about how to draw pedigrees using DOT.