I saw a link today to an HBR article that seems to contradict the 'Build Indisciminately' advice on networking:

The article seems to be suggesting that large networks aren't useful and may even be harmful and the 'cost' (in terms of time) of maintaining a large network may cut into other, more valuable, things. 

I'm also a little concerned that it seems to be very much concentrated on networking websites like Facebook and LinkedIn (both of which I love and use pretty much every day).  As I see it, whilst there's a good chance that many of your network will be conencted to you on one or both of those sites, your Facebook Friends and LinkedIn connections are not your network.