Opening your organisation up to blogging or wiki's is difficult for many organisations. It flies in the face of traditional management control over messages and information. It opens the organisation to all sorts of crazy or litigious things that people may write.
Your milage and details will vary, but the basic argument for the safety of open internal enterprise collaboration goes something like this:

1. Anything people publish will have their name on it.
2. Is there anything an employee could write on their blog or a wiki that would create a problem for your organisation but does not breech existing policies around communication, confidentiality, etc?
   
   If so, is that a problem with blogs or a problem with your existing policies?
   
   
3. If an employee breaches communication policy, is it more likely to occur in email or on a public forum?
   
   Which would you prefer, one you can see and act on or one that is hidden and may surface in the future?
   
   

Beyond all the policies and controls, your employees aren't idiots and should value their job. (If not, that's two good things to find out ASAP anyway.)

After finishing my MBA at MGSM back in 2005 I'm finally ready to talk about it...

I did 16 subjects, 16 exams, 16 groups, ~48 assignments, thousands of pages of reading. I recall almost none of it.

But, as a result of my MBA, I am self-aware of my style in groups, confident in my breadth of knowledge and able to see business from different view points. I can make hard decisions more easily and am comfortable finding a balance between performance, friendship and opinions.

Oh, and having the piece of paper doesn't hurt either.