I just created an OpenID account using MyOpenID (which is run by the guys who developed one of the top libraries for OpenID, in Python of course). After reading Simon Willison's blog entry on OpenID and noticing that Ma.gnolia used it, I figured I would give it a go.
It was very painless. What was great about it is that I was able to open a Ma.gnolia account without specifying anything! My OpenID account handles the authentication stuff (so no password required for Ma.gnolia) and they then gave Ma.gnolia my email as it is required to sign up so I didn't even need to fill that in. I wish all account creation was that simple!
And although I have barely used Ma.gnolia, I have to say it is a very slick site. The interface to the site is very intuitive and they seem to provide all of the features I want for a bookmarking site.