GENi

My Aunt referenced me to the site GENi.  GENi is a free genealogy website where you can create your family tree and invite your family to continue to fill in the details.  The interface is very easy to use, which is good for when the family historean and the family computer wiz are not the same person.  You can enter dates for any special events for your family, including births, deaths, weddings, and any other occassion.  You can upload photos and videos and tag them to members of your family.  

As far as privacy goes, GENi describes who can see your profile based on degrees of seperation.  Anyone who is fifth cousin or closer is one security level.  Beyond that is a second security level.  People you mark as friends are in a third security level, and then there is a fourth, final security level that applies to everyone.  In this way, you can keep your family tree private from the entire web world, and expose different levels of information based on how closely you are related.

GENi is particpatory, so the results of your family tree are going to vary based on how much of your family history you know, and how willing your other family members are to enter additional details.  GENi does not perform any research for you.  Our tree is pretty interesting because my grandmother, aunts, and uncles have already posted a number of photos and entered details for my ancestors that I never knew.  I've augmented the tree with additional people not already listed.  In doing so, whenever I attach an e-mail address to a new family member on the tree, that person is invited to add new details.

I spent entirely too many hours the first night browsing the tree and expanding on family members.  If you enjoy genealogy you will probably like this site. (http://www.geni.com/)