There are official blogs, like Jonathan Schwatz of Sun and others that are corporate preaching/marketing/promotional efforts. Not that this blog or others aren’t what the authors think, but I feel that they are probably checked and monitored by someone at the corporation to be sure that the message doesn’t bring any liability or unexpected issues out.
Then there are unofficial blogs, like the guys at MSDN that are handled by employees, they are asked to post, but they are not really monitored. I’m sure there are guidelines and regulations, however, that have been posted, emailed, snail-mailed, etc. to everyone.
I ran across this article on potential legal isues with blogs on eWeek. It doesn’t appear the courts have been involved yet, but I’m sure it’s coming. At some point there will be someone that sues or gets sued over a posting and then we’ll really find out how “private” those blogs are.
I made a note on the SQLServerCentral blogs page, but it’s something to think about whether you use a corporate site or your own private one. Be wary of what you post in a blog. To me the same rules that apply with you at Happy Hour apply on the blog. If you don’t want it getting back to your boss, don’t post it.