To me Network, like Instruction from the Mercenary book, is just poorly thought out fluff to fill pages.
The use within the book is a bit sporadic. I can make no sense of why some specialties have Network in their skill table and others don't.
Like nats said, Street, Corporate, Political, Criminal, Military and Academic networks. So why can't folks actually from those careers establish networks too? Do we need to go retcon all the careers to add networks now?
Didn't we already have allies and contacts in the CRB? The Agent book does make use of them. Why do we now need networks too?
We were discussing the aforementioned Instruction in a thread a while back and someone from Mongoose indicated that they would not be adding it in a rewrite of the book. I think Network should receive a similar fate. Personally I'd re-roll if these items come up during chargen.