I'm also quite skeptical about Disqus from a number of aspects, but this is a very interesting feature, with the potential to do for commenting what github is doing for code hosting - i.e. explode it to a new level.
Disqus are really doing some good stuff here. At first I was quite sceptical about Disqus, but actually, it's a useful service from the point of view of the user. Disqus has the potential to become the thread that links together a bunch of blogs into a real community.