Just consider this (perfectly valid!) case: I, a German blog owner, blog about immigration issues and my blog post attracts a couple of US neonazis which use the Hitler salute, which is legal in the US, but forbidden in Germany.
As I am not in control of the comment server, I cannot delete the offending comment and protect myself from legal problems (it's a criminal offence after all).
Obviously the same problem arises for copyright violations - anyone remember the spread of the HDCP masterkey?
My personal inclination is to accept any comments from people I know, and notify myself of any from people I don't know. I can then approve them/block them by adding them to my address book.
I can see a proof-of-work system working reasonably well (gets rid of mass-spams, though big sites would still get automated ones), but it seems like there should be something baked into it if this is at all intended to grow beyond 'indie'.
The advantage of Disqus is that I have to check only one dashboard and instantly follow track of the conversations at >20 web sites. It's like Google Reader, just for comments.
If so, i'm all for it.
Dealing with the administration is hard though. Hosting comments is easy, brain-dead CRUD stuff but then you've got to manage spam control, post rates, SEO and questionable content.