Web site registration is usually more stick than carrot. The worst sites are those that require you to register before providing any indication of the benefits that will be accrued from entering yet another username and another password. (Bring on OpenID and single sign-on).
Geni.com breaks that rule of not placing a registration barrier before customers can interact with your site, but they get away with it. How? Registration is hardly a barrier – it is only a request for an email. The first page you view visually articulates the proposition, compelling you to continue. To add an email is hardly an onerous task. There’s no request for password, no T’s and C’s. The password is covered by the email they send you, and do we really need the small print that no-one reads anyway… Besides, logging in is only relevant the next time you visit the site, by which time you will probably already be committed. Not only is proposition itself is really compelling, the execution is excellent. The guys behind this have obviously spent some time thinking about the design and the usability. They could easily have jumped on the community site bandwagon and built something to obtain VC investment. But they’ve gone one step further and built something that engages not only on content, but also on interaction.