The thing about Disqus that bugs me is its branding. It puts its name on every page thrice and its url twice. Because registration is so front-and-center on its comment form, I feel disinclined to use it to post. Furthermore, despite claims that it can be really well integrated, every time I see it it stands out - not really terribly, but I hate being able to instantly differentiate it from other comment systems.

Also, something about the up-and-down buttons piss me off. They look too grubby. And since they look the same on every blog, that quickly gets annoying.