A downside of OpenID is that you can’t choose the site to link to. Most of the time the site is actually your login URL. This can be solves with so called delegating. It means that you paste some code in the header section of the page you want to link to when using your OpenID account.
For my OpenID account, provided by Launchpad, I’ve added this code between <head></head> in /wp-content/themes/qense/header.php:
<link rel="openid.server" href="https://login.launchpad.net/" />
<link rel="openid.delegate" href="https://login.launchpad.net/+id/xxxxxxxx" />
<meta http-equiv="X-XRDS-Location" content="https://login.launchpad.net/+id/xxxxxxx/+xrds" />
This code comes from the Launchpad help page for OpenID. Of course, I replaced xxxxxxxx with my OpenID id. Now I can enter http://www.qense.nl/ when logging in with OpenID.
Now I just have to find a way to couple my WordPress account to my OpenID!
EDIT: I’ve just found out how to add OpenID accounts to your WordPress account. Just go to your profile and add your OpenID URL to Your Identity URLs. You have to login with that account to confirm it and you can login with that ID too.