I am more open about personal stuff (kids, etc) on Facebook. Twitter and G+ I use for academic pursuits. Not to say that my personal life doesn’t affect my professional life (it does very much so); however, most of my friends on Facebook wouldn’t even know about anything about my professional interests. It’s easier that way.
The emergence of G+ has be thinking about if this separation will end as more and more of my friends join G+. To have it all in one place would be great, but I would still separate those two purposes.