Blogging can be a very useful tool in the workplace. It can also be very damaging. It amazes me that people think they can say anything they want without there being any consequences. Anyone who divulges private company information on public forums can rest assured, that if seen by the their superiors, they will be held accountable. I would assume that the majority of people that are willing to jeopardize their jobs in this way, probably are not the most valuable employees.
The important thing to remember, when blogging about work issues, is to use common sense. If you wouldn't say it to your boss or announce it over the radio, then you probably shouldn't post it on a blog.