Check this out. As the article rightly points out, lots of people tend to confuse "right to blog" with "right to blog without negative consequences." In the U.S., First Amendment rights protect citizens from prior restraint. But they don't provide for consequence-free publishing.
Cases are usually pretty clear cut when dissemination of confidential information is involved or when "at will" employment is the norm. Bloggers have a right to post about their companies, but employers have the right to discontinue their employment.
Personally, I'd encourage any employees of Underscore to blog. But they'd have to understand some basic ground rules first, like restrictions on confidential information and things like that. But not all companies take kindly to being written about by their own employees.
In the age of citizen publishing, it probably makes sense for companies to provide policies and guidelines concerning publishing projects outside the office. At least that would head off most potential problems or misunderstandings.