Based on personal experience, I advise anyone who asks not to put a tree on geni.com.
To put it simply, you lose control of the tree. I've had several instances of requesting others who've added clearly, almost laughably, wrong information to the tree, to correct or remove it, who have refused to do so. I once tried to delete the tree, only to find that once someone else has latched onto it, it can't be deleted. One's only option is to close one's account, but that doesn't delete the tree -- it remains. I decided not to close my account, just so I could see who was doing what to it.
My negative opinion of geni is not a matter of "religious belief," as one commenter has suggested; it's based on objective fact and experience. And as for the idea of a "one world tree" of all humanity, well, ....
Stephen Katz

Web sites I manage - Personal home page, Greater Houston Jewish Genealogical Society, Woodside Civic Club, Skala, Ukraine KehilalLink, Joniskelis, Lithuania KehilaLink, and pet volunteer project - Yizkor book project: www.texsys.com/websites.html