I am sure this is a well documented problem, but I just got this from our Communications department:
“There is no reason why you cannot keep a personal blog in your own time, but we would ask that you did not mention who you work for on this. The same rule applies for social networking sites. There should be no discussion of (my employer) affairs on blogs/social networking sites. We have a blog that you are welcome to feed your thoughts into, email your content…”
Well now I know!
I posted this in my lunch break BTW 😉