I love the convergence of online and F2F networking, whether strictly social, professional, or a combination of the two. However, I do find it amusing when someone adds me as a Facebook or LinkedIn friend and then barely recognizes me when we meet F2F.
So, my one piece of advice would be: Take the time to get to know people in the flesh as well as online--don't let a robust online network take the place of real, meaningful F2F connections.