Personally, I know that none of my family is using Geni right now, but they enjoy the birthday emails and I'm not doing it for them anyway. I want my kids to know where they came from. My grandfathers brother called me on Friday. It was the first phone call that I ever received from him. (We've spoken and see each other, but really just at family functions). He called me because of the emails that he has been receiving form Geni and I ended up getting a lot of family information from him.
It's a very useful tool for many different reasons.