It could be a useful resource - website-reference, listing all the OpenID providers along with the features they support - SREG and/or AX, PAPE policies, etc.
Are there any?
It still lacks a lot of (major) providers, but this could be a good starting point.
I'm surprised because this table gives the impression that sreg is far more developed than ax, although, from my own experience, both Yahoo! and Google use the later.