Like any on or offline networking, the value you get has a direct relationship with the value and time you put in.
My Facebook profile has generated old friend connections, new connections, activity on my forum, attendees to my events including Your Brand Radio and has been the source for some Strategic Career Plan Sales. I finally started spending time on Facebook at the beginning of this year (five months ago or so) and happy with what is happening already.
The almost daily value I add and ultimately receive on
LinkedIn is greater because I have more years there with significant contact and activity.
You will see stories like mine and stories with much greater value and far less as well...there will be a relationship to the quality of your profile and time you take. I hope this helps.