Each of these tools has it's own suite of tools, networking advantages, privacy concerns and other nuances that need to be carefully navigated. This can be managed but only by careful consideration and planning.
I cascade and quarantine my social networking a couple of different ways. For one I use LinkedIN for professional stuff (ala public CV and professional reflections), Twitter for public broadcasts (ala education shares and blog posts) and Facebook for personal stuff (ala family and friends). I mention that I cascade information as all my LinkedIN status updates are automatically forwarded onto Twitter, then all Twitter posts are also forwarded onto Facebook. This does not happen the other way around.
Where I cast my stone into the Internet pond, I try to arrange things so that the information ripples will spread only to and where I want it to. If you do the same, keep your eyes wide open if you are going to enjoy the splash.