The relationships you have with people around you are your network. Your network is made of both "personal" and "professional" connections -- it doesn't really make a difference. The stronger and wider your network, the more opportunities it will bring to you, and the more it will be able to come to your aid when you need it. This network is your career insurance.
The internet is made of people and relationships. Before being another "channel" for the usual marketing and communications (this is for brands), it is a space we humans live parts of our lives in. We create relationships when we spend time with others building, sharing, connecting, loving, arguing. These relationships enrich our network.
Our online presence is our digital self, through which we interact with others. It is the key in the online world to strengthening and growing our network. But for that to work, our online presence needs to be us, not some construct designed to achieve a specific goal (personal branding). Think about when you're having drinks and mingling after a conference: it is your humanity that connects you with others (networking). Not a communication plan. Not a brand. Not a message. Not a strategy.
Being authentic online can be scary. We have been told again and again to be careful what we share online. We often are wary of mixing professional and personal. We don't see how precious our personal connections can be for our professional life.
Almost twenty years building the social web have taught me that when it comes to being online, the more you give and the more you dare, the more you get in return.