SF-based Geni launched a few days ago and I played with it for about two hours. It is VERY addictive! I loaded up 54 names over 5 generations...inviting my family and extended family (if I had their e-mail addresses). It took a couple of days, but a cousin's wife began to extend the tree. I have a lot of cousins and they have been quite busy these past few years passing on their genes and I (sadly) don't know all the names of all my new second cousins. Now I will...provided they all start to add to the tree.
My only question is what happens when individual nodes meet one another...do they automatically connect with one another? [Update: just read that trees will eventually merge. Very cool!]