Twitter: knowledge builder or time waster?

I am not much on twitter, I do like the site is just that I don't really like the idea of telling people what I had for lunch or dinner very appealing. However some people do know how to use tweet for their own advantage. You know a close friend of mine uses twitter to get referrals and to promote his websites and he gets good results, don't know what's his secret though. I guess it depends on what you want to user twitter for. If you want to tweet about your life, well that's a waste of time you are not getting paid for it, you could mylot instead of tweeting.