Simon Owens of Bloggasm has conducted an unscientific survey of diversity in the blogosphere by emailing a bunch of bloggers to ask them demographic questions. He emailed 1,000 bloggers, and on that basis, has constructed a quick profile of the "blogosphere":
Male: 69%
Female: 31%
***
White/Caucasian/European: 73%
Black/African: 9%
Asian: 10%
Middle Eastern/Arab: 1%
Latino/Hispanic: 6%
Native American: 1%
Make of that what you will.
The flaws in this study are many and obvious, and Simon is up front about them. Flaws aside, he deserves credit for even attempting to do this sort of thing. So go take a look at his post, which contains lots of other stuff-- breakdowns by blogging niches, comments by big-name bloggers, discussion of the methods and flaws.
(Full disclosure: I was one of the people surveyed, which is how I know about this in the first place.)