Good read over at ComputerWorld. Much if this falls into the category of "anonymity breeds irresponsibility":
"It's probably a good idea not to allow truly anonymous use of an internal blog. (IT professionals can configure internal blogs so that all users can be identified, at least by the company.) Anonymous speech has certain advantages for would-be whistle-blowers, but there are other ways to report things anonymously without resorting to blogs. As a general matter, the potential for anonymous speech creates an atmosphere that can encourage irresponsible behavior, such as harassment, defamation and gossip. Except where there's a clearly identifiable benefit, anonymous speech in the workplace should be avoided."