Simplified (Inaccurate) Background About OpenID
Some websites allow you instead of registering and logging-in (meaning re-entering the same information you entered before in so many other sites), to enter what is called Open ID URL, which is a URL given by a another website that you already logged in and has your information (called OpenID provider).
Once you enter the URL and continue, you get redirected to the OpenID provider confirmation page whether you want to be able to login to the new website using the same login,which gets redirected back to the new website but this time as logged in user.
If your OpenID provider is a popular provider, like Yahoo or Google or so, some websites will give you a shortcut to writing the URL at login by just selecting the provider from a predefined list of providers in the login page. If your provider is not in the list, or the website does not offer any shortcut list at all, you should be able to know your OpenID URL to enter same as you know your User ID or so.
The first relation between Google and OpenID started with Blogger. It first accepted logging in to write comments on Blogger using OpenID, and had Blogger itself become an OpenID provider (you enter your blog URL as your OpenID URL). Why Google did this to Blogger accounts only not all Google Accounts (used for Gmail, etc..)? I don’t know. I think this is because Blogger accounts were not yet merged with Google Accounts at this time.
Later Google as a whole became an OpenID provider for all Google Accounts (AKA Gmail Logins), with different OpenID URL. This means if you have Blogger account, you have two different OpenID URLs offered by Google each maps to DIFFERENT LOGIN. Again, maybe because of backward compatibility or whatsoever.
If your real blog is not on blogger, and you use your Gmail account primarily, you may want to use the Google Accounts Open ID URL as your OpenID login to all websites that support logging in with OpenID, but, unlike the easiness of remembering a Blogger blog URL, the Google Accounts Open ID URL is a bit ugly and you might not know about it.
Well, here is the Google Accounts Open ID URL (yeah, the entire blog post is about this single line):
Note: You do NOT replace the part "ID" with your Google Account user-name/email. The OpenID URL is "AS IS" above whatever the Google Account ID is..