The Globe and Mail has an article up on an Ispo Reed poll in the US about blogs.

2,537 US adults were surveyed. 30 percent had read a blog at least once.
More people in the western US read blogs.

More than half of blog readers felt that blogs were accurate and 68% believed blogs had an influence in public opinion.

It would be really interesting to see studies in other countries and regions - Asia, Europe, Australia, the UK.