with facebook you can get in touch with people that might be othwerwise unreachable (it allowed us to do a proper high school reunion for example).
the key is to use it sparingly and not spend too much time, it has some addictive factor in constant news feed that make news sites look like static HTML pages. it can be a good tool but a bad master
linkedin is purely professional, basically your online CV + network of your colleagues. they tried to make it more FB-like but I don't know a single person who is not recruiter who actually ever checks that.
the key is to use it sparingly and not spend too much time, it has some addictive factor in constant news feed that make news sites look like static HTML pages. it can be a good tool but a bad master
linkedin is purely professional, basically your online CV + network of your colleagues. they tried to make it more FB-like but I don't know a single person who is not recruiter who actually ever checks that.