Here is an interesting article that shows that almost 1/3rd of active Internet users in Canada have used a blog in the last 3 months. While the study was performed in Canada, you can probably safely extrapolate those numbers to just about any industrialized country in the world and it would be fairly accurate representation of blog use.
The article mentions that blogs are a double edged sword. On the one side it gives companies a great way to spread information about their product and services as well as feedback from customers, but on the other side it gives customers a great way to spread complaints. Finally, it mentions that blogs can be written by professionals or amateurs. Let me just say that if you are a company wanting to use blogs as part of a marketing campaign that you don't hire amateurs. Not to say amateurs can't write well or help boost existing marketing efforts, but they should never be the marketing effort.
For an effective blog strategy to work you need to formalize it as you would any marketing or PR campaign. You also need to use a professional writer to help develop the content for the blog. Finally, you need an Internet or marketing consultant that can help you integrate this into your existing marketing and PR efforts and make field adjustments along the way to get the most from your investment.
Here is a link to the full article
Michael Temple