While we may be biased, I've never noticed any sites I visit using IntenseDebate. Perhaps it's less branded than Disqus and I just don't recognize it? Or maybe the circles I run in just tend to favor Disqus?

I don't know about how much of a bias HN has. A lot of people are openly critical of HN products when they honestly don't like them: I'm often critical of Reddit, for instance, which was one of the first big things here. And in many cases, I don't know what companies are YCombinator and which aren't. Meanwhile, a lot of services that do get a lot of praise here aren't actually part of the incubator program.

In this case, Disqus is simply more used. I've never seen IntenseDebate outside of its web site, though I prefer its aesthetic look a bit more. I don't like the colloquial "Easy Tiger" message when you're not logged in, though, so it balances out.

...until IntenseDebate's functionality is integrated into WordPress.

To be fair, it seems to have had a year's head start.