I'd follow them on twitter because it's a place to get people's opinions whether you know them or not. But facebook is for chatting with friends!
Now that's a point, Steve. Does it depend on the media? Are there places that we really just want to keep personal, or are we in public wherever we are online?
Oh God! I have about 50 politicians as friends on Facebook. Most of them don't even interact with their friends though. Twitter is much better for 'following' your elected representative. Or TheyWorkForYou.com to keep track of what your MP is doing in Parliament.