please don't remove support for openid! if myopenid.com is down then it's really easy to set up an open id at a different provider, and open id is so much more flexible/secure than having a logon with a separate password, risk of password database compromise, and no support for two factor authentication (which I use with Verisign PIP).
I agree, it would be a shame to see it go. Perhaps you could leave it as an alternative option for more technical users?
That would probably save you the hassle of migrating all the existing accounts as well.