This
Fortune article discusses how corporations can use blogging to get their word out - and how to cope with their employees blogging. One quote:
Don't shut down existing employee blogs. If they are positive about the company, Rubel suggests turning these evangelists into a voluntary sales force. If they are negative, you might have a larger morale issue that needs to be addressed.
This is so NOT the experience of people I know. But then,
The most important question to ask is whether your company should even blog at all. "There are some corporate cultures where blogging is not going to go over very well," says Sifry. Cultures where blogging thrives, he says, are ones that "have faith in their employees, rather than fear."
Trust is part of it - but so is an organization that's organized enough to know what it wants & how to do it.