From the September 24, 2009 New York Times, in an article about Twitter raising money, and their ability to generate revenue:
“It would be trivially easy for them to turn on a revenue source today,” said Steve Broback, founder of the Parnassus Group, which runs conferences on Twitter and other business topics. “I don’t see that they are in a big hurry to start generating revenues, mostly because they want to minimize any sort of negative effect on their community.”
So in fact, what Mr. Broback is saying is that it would not be trivially easy for Twitter to turn on a revenue source today.
Just wanted to clarify that.