First, I'd like to know, 'Compared to What'? I teach on a faculty that has far fewer women then men, so I'm prepared to believe there is a fair amount of sexism remaining in society. (On the other hand, we have had three female Deans in our fairly short history, including one whose ghost all but still walks the halls, so it's not all bad news here.) So the question may not be “are blogs sexist” but rather “to what extent to do blogs replicate or transcend existing patterns of behavior”.
Obviously, it would be great if we could show the flowering of public discourse to be a Habermasian public sphere operating without coercion or prejudice. But that is not very likely. I'd settle gladly for the news that the online exchanges are relatively less sexist and relatively less irrational.
No one in his right mind thinks that blogging, or the Internet in general, is free of strategic behavior (like, for example, frivolous threats of lawsuits). It stands to reason that when we “go online” (actually write stuff for public consumption), we are more or less ourselves. But it's also conceivable that, as group norms evolve online, and as communities of discourse form and re-form and cross-pollinate, we can grow and change, and collectively become more than what we were.