You are likely a member of Linkedin. There's almost no chance you don't have a Facebook account. A few of you, and many more later, will spend time with Gen.Connect.com (a nascent "expert" and "community" sight) and others.
All of you have a roll-a dex of one thickness or another. Many use Salesforce.com and/or Constant Contact. Why do "we" commit to those activities? Some do it out of fear or loneliness. Most do it to seek out opportunities; a job, a better job or perhaps a consultancy. Most, when offered the opportunity to "connect" with someone new, check out the requester profile first, to ascertain what potential benefit might accrue with an acceptance.
So what do we have here? It appears that the prism through which any professional "networking" activity must pass through is "what's in it for me?".
There's another way to think about this. The more people with whom you intereact, the more people may benefit from their association with you. If your true mindset is "what can I do to help?" and your behavior reflects that, what do you think that says about you? You hit the "accept" button and in your reply, the message you send is along the lines of, "I'm delighted you reached out to me. I look forward to connecting with you and seeing how I may be of service." Corny? Only if you don't mean it.
Think about the reputation you acquire by relating this way. You become the default person, when the question comes up, "who might be a good source of work, advice, counsel," etc. for this unique work, I need to fill.
Love Your Work and Work Tirelessly
Communicate Honestly and Fearlessly
Serve, Don't Sell