Permanent email
My cousin has a “permanent” email address through her college. But, as it turns out, the college got tired of email hosting, so they’re not going to do that any more and plan a new Web 2.0 social web service instead. This is nice and shiny, except that my cousin actually counted on the permanent email address being, well, permanent.
I expect this will be a more common problem as we renegotiate responsibilities for Web services. And I think there’s a long-term problem with domains and naming; I can imagine a dystopia where domain ownership becomes a sort of hereditary nobility.