Geni.com just launched. It's a family-tree-making service that's easier to use than any other competing system I've seen. And it's free. It also has a straightforward way to invite other family members in the hopes that they'll put in their own data.
I covered competitor Amiglia last year. Like Geni, it has a Flash-based interface for adding people to your tree as well as for navigating it. Geni is not as snazzy as Amiglia, but it is much easier to use. Data entry is a snap, because when you're first building the tree, the only data you have to actually type for each person is their name. Relationships are encoded by clicks of the mouse, and you can fill in other data (birthdates, whether the person is alive or not, and so forth) later.
You can enter e-mail addresses when you're doing your quick first pass, and Geni will then (optionally) invite these people to contribute to the family tree with info you don't have. The system is easy enough to use that I would not have qualms about inviting nontech-savvy relatives.
However, Geni's ease of use comes at a price: Its simplicity leaves out methods of coding in single parents, for example. It's not a tool for professional genealogists. But it's the best thing I've seen yet for people who just want an easy way to record their family tree. It's a lot of fun, too.
See also: Social networking, circa 10,000 B.C.E.