I've noticed that there is a very dramatic difference in the user experience for sign on with different relying parties. I've implemented a few relying parties myself, so I already have a few ideas, but I'm curious to hear from other people about what worked, what didn't. Empirical evidence (OpenID login stats before/after) would be ideal, but anecdotal stuff is fine too. Even small tweaks would be interesting.
How much does the identity provider factor into the equation? Yahoo's implementation is obviously terrible, while myOpenID's is pretty good. Verisign's is vault-like, and I'm starting to think this compromises the user experience significantly. But what about others? Have you seen users having more issues with one provider versus another?
What best-practices, if any, can be derived from this?