I saw one of Amazon's UX team at a talk a while back, and the way he described it is they have a set of actions/permissions for people who are totally logged out, a set for people who are "sort of logged in", and then a set that require full login.
It's definitely tricky to implement (how do you determine whether a user is "sort of logged in"?), but once you get over the conceptual hurdles it's a pretty awesome user experience.
However, I would argue that like much of what Amazon does, it's not necessarily appropriate for the majority of sites.
It's definitely tricky to implement (how do you determine whether a user is "sort of logged in"?), but once you get over the conceptual hurdles it's a pretty awesome user experience.
However, I would argue that like much of what Amazon does, it's not necessarily appropriate for the majority of sites.