You could even have the same comment-conversation appearing on multiple different websites.
One of the things I find frustrating about comments is that the same conversations come up repeatedly. Why not build on what's already been said instead of wasting time repeating the same points?
On websites which receive numerous comments (I'm talking pages) this would make a massive difference.
Every Disqus user has an activity streams on disqus.com itself. Unfortunately, this activity stream is usually pretty baffling because the comments don't make sense outside of the context where they were posted. Yoomoot's Q&A format means that posts usually do make sense even when isolated from the wider context.
('post summary' being the maximum-111-character title that every Yoomoot post has.