Corporations generally are blocking access by their employees to parts of the Internet. And it's not just corporations, but libraries, schools, and parents. There's several reasons, for example parents wanting to prevent their children from seeing horrific or sexualized websites.
No Longer Safe for Work: Blogs (October 24, 2005, Christopher Null, Wired News)
The article talks about a lot more than blogging. A great concern by corporations is leakage of "confidential" information, as well as virus or phishing attacks on employees. I know from my job environment, virus's can cause us a lot of employee time to fight the virus infection (rather than get work done) and it would be a huge black eye if our product shipped with a virus infection.
But, the corporate firewalls in some cases are now filtering any "blog" from being read by employees. Not every corporation is doing this, but enough are to cause the above article to be written. Supposedly blogs are time-wasting activities, and the corporation wants their people to focus on the job. But... I ask... What if the employee needs, as part of their job, to find information on the internet, and what if that information is on a blog?
There's nothing special about blogs that make them distinct from other web sites. Blogs can hold useful information just as easily as they can hold time-wasting drivel.
e.g. What if the corporation in question has servers made by Sun Microsystems? It's well known that Sun has a blog site that's full of postings containing useful information about Sun's products. An employee of such a corporation would clearly need their employees to access blogs.sun.com, yes?