I was curious today and decided to try out the LiveID and OpenID integration with my site. In general, it was suprisingly easy. I enabled them both in my Host Settings, then activated them for the portal in Site Settings. Setting them both up to use the service was also easy.
What was really frustrating was that I could not associate my shiny new OpenID identity with the appropriate user I had created within DNN. The reason?
Apparently you can only associate id's that are not Admins or Host accounts. So I had to create a normal user account, and then if I wanted an admin give it the access afterwards. For it to be a Host account I had to manually set the account in the database (set IsSuperUser=1 in the Users table for the appropriate user).
A minor inconvenience, but the error messaging could have been a lot more helpful.