First of all, do user tests yourself.
It doesn't require special equipment: any screen recording software will do. You can run the test on any website you wish. Choose the one you think implements OpenID most conveniently.
You can gather people from the streets, friends (acceptance criteria: no degree in IT or Math or Physics, not even BSc), or in a pub.
Or you can do it remotely, through Skype or Hangout or join.me, offering 10 euros on a local Craiglist or something.
Here's a video on how it's done. There really isn't anything more into it. Just make sure you:
- Don't explain
- Don't show
- Don't help
Just ask questions (mostly starting with "why") and ask the participant to think aloud, and make sure they understand it's not them who are tested but the website in question.
That's it, really.
Personally I think it's a consistency issue (this is not how "internet" works), and also a trust issue, but I haven't done usability tests in this regard so far.