Whether a company blogs in-house or out depends a lot on internal resources. Although they are inexpensive in terms of software and programming, blogs take considerable time to write and market. For example--
Posting on a frequent basis attracts a steady audience. You should strive for at least one post every workday.
Responding to comments is a good problem to have if your blog becomes popular. Promptly getting involved in online discussion of your own posts attracts and holds your audience.
Building a blogroll. Links and information are valued in the blogosphere. Most blogs have a list of favorite blogs, or a blogroll, on the sidebar. For many visitors, a helpful blogroll may be as important as your actual content.
Social networking is sometimes the most effective way to build traffic. By visiting other blogs, leaving comments, and striking up online business relationships, you encourage other bloggers to visit your site and recommend it to their audience.
Active search engine marketing likewise builds an audience, often in a big way. Common SEM techniques include optimizing content (especially on headlines and hyperlinks), registering with blog directories, notifying search engines of updated content, and managing and promoting subscriptions via RSS feeds. (Get some ideas from blog guru Steve Rubel on how to use RSS feeds.)
If you or your staff is ready, willing, and able, running the blog in-house has advantages. No one from the outside has your industry, company, and product knowledge. Writing posts from the inside adds a level of authenticity and openness visitors crave.
On the other hand, outsourcing to experts saves time and delivers a more professional-looking and more effectively marketed blog.
As usual, the soundest approach is somewhere in between. A workable mix is to hire reliable outside talent for content development and SEM, but maintain editorial control on the inside. Often, writing responsiblities can be shared among employees and outside writers. As long as the company has a blog champion, any combination of resources can get the job done.