Been having issues with stackexchange creating weird usernames for me and grouping them with my account, it appears to be a known issue, and emailed the stackexchange team... which leads me to my questions, I'm looking for usability studies of user authentication methods and interfaces, do you know of any?
I can tell you from our experience that OpenID is a giant impediment to signups. I don't have hard numbers to back that up, only anecdotal advice from
At the Business of Software 2010 conference, one of the attendees had done an A/B test to guage the adoption of OpenID vs. google, facebook, and username/password. The only statistic I remember is that of the 1500 data points for signups, zero were from OpenID.