Nat Sakimura, who is quietly implementing real user-centric identity solutions in the Japanese market while many others are still talking about them, has posted his concise reasoning why XRI abstract identifiers are the the only really safe identifiers to use with OpenID.

The whole question of the differences between abstract and concrete identifiers, currently being explored in depth in conversations between the W3C TAG and the OASIS XRI TC, may turn out to be a crucial one for the soon-to-begin work on OpenID 2.1. When it comes to security, privacy, and usability, the differences really start to add up.