The real money is in targeted advertising — you could pitch ads based upon the keywords of the tweetstream. The trouble is that next to Facebook Twitter hasn't really worked at this. On facebook within 24 hours I can be running an ad campaign with highly sophisticated tools on a budget of $25. If I only have $25 Twitter doesn't seem to care that I exist, in fact they only start to care if you've got $60k a year to invest in ads: http://business.twitter.com/advertise/start