You probably thought of this already, I trust there is even a topic created. But I couldn’t find it.
Now, I now Disqus ain’t exactly open source, but I think Wordpress do offer a global login. If it’s all opt-in, for the site owner and for the user, it should be fine, shouldn’t it?
I’m talking about the notification balloon up top, something like we have on StackExchange network, where we get notified for every site we belong. Makes sense?