<p>I have more than one OpenID as I have tried out numerous.  As people take up OpenID different suppliers are going to emerge I may want to switch provinders.  As all IDs are me, and all are authenticated against the same email address, shouldn't I be able to log into stack overflow with any of them and be able to hit the same account?</p>

I think each site that implements OpenID would have to build their software to allow multiple entries for your OpenID credentials.  However, just because a site doesn't allow you to create multiple entries doesn't mean you can't swap out OpenID suppliers.
How to turn your blog into an OpenID
STEP 1: Get an OpenID. There a lots of servers and services out there you can use. I use
http://www.myopenid.com
STEP 2: Add these two lines to your blog's main template in-between the
```
<HEAD></HEAD>
```
tags at the top of your template. Most all blog engines support editing your template so this should be an easy and very possible thing to do.
Example:
```
<link rel="openid.server" href="http://www.myopenid.com/server" />  
<link rel="openid.delegate" href=http://YOURUSERNAME.myopenid.com/ />
```
This will let you use your domain/blog  as your OpenID.
Credits to
Scott Hanselman
and
Simon Willison
for these simple instructions.
Switch Your Supplier
Now that your OpenID points to your blog, you can update your link rel href's to point to a new supplier and all the places that you've tied your blog's OpenID will use the new supplier.