A release from marketing advisory firm Warrillow & Co. (not available online as far as I can tell):
While celebrities and the under 25-year-old population are flocking to Twitter, small business owners are just realizing the full potential of blogging. Use of blogs for specific business purposes more than doubled in the last 12 months, and 40% of small business owners now use this medium in their business.
The April 2009 survey that produced this finding was based on a survey 1210 U.S. small businesses with less than 100 employees.
Note that when they say "use," they don't mean actual blogging by small-business owners; they mean readership of blogs by small-business owners. But it's probably reasonable to think that more business owners reading blogs will lead to more tempted to write their own blogs.
But small businesses are overall still way behind the curve on Web 2.0--they still haven't mastered Web 1.0. Warrillow previously published a survey that found that only 41 percent have webpages. Read more here.