One of the things that I like about Automattic's Stats plugin is that it actually makes my WordPress.com account aware of WordPress blogs that are not on WordPress.com. I find it useful because although my main blog is not on WordPress.com, I do have a few on WordPress.com, and I can identify my primary blog as the one that isn't on WordPress.com. (It's also really nice to be able to see information about ALL of my blogs, including ones that are on AND off of WordPress.com, in one place on my Global Dashboard.)
I'd like to see the self-hosted version of WordPress be able to integrate with the Global Dashboard on WordPress.com in this way (obviously as an option, as some people might not like a "call-home" feature like that), so that WordPress.com can be like a central "hub" for all of my blogs, including ones on WordPress.com, ones on other websites, and blogs on WordPress MU installations. WordPress.com's OpenID support could maybe be helpful in this area.
Feel free to contact me if you want a more specific description of this suggestion and other possible ideas that could tie into a system like this.