Reverse in Time
Companies that made websites in the early days of the internet enjoy much higher search engine rankings, simply because they've been around longer than anyone else.
It's the same with social networking. You can begin to build a presence now so that when everyone catches on and starts scrambling for relevancy, you will have a huge leg up.
As of February 2009 Facebook gets nearly 1.2 billion visits per month, and Twitter gets 54 million. Go where your customers are.
Personalize Your Company
The days of hiding behind a well-crafted and managed “brand” are over. Crafting an artificial image of your company was easy when your customers had no way to interact and talk about you.
Now they can. By joining the conversation, you can address any positive or negative feedback immediately.
Your company is made of up of people. Let that shine through. People connect better with other people than big faceless brands (that's why friendly sales people are so effective).
Putting the humanity back into your company helps forge customer connections.
Brand for the Long Term
Social networking users usually haven't even begun the buying process for your service. But that doesn't mean that connecting with them doesn't have value
If you have regular contact with a large group of your demographic over an extended period of time, when the time comes for them to buy your product/service you'll be first in their minds.
Compared to a mass-media campaign, branding on social networks is ridiculously inexpensive.
Invest in customer engagement now and reap the benefits later on.