“Calacanis makes the obvious riposte: in-stream advertising. No one is going to object to an occasional ad tweeting by, if the service is free.”
Calacanis is wrong. The moment I start seeing ads in my Twitter stream is the moment I stop using Twitter. I’ll happily pay a fee every year to avoid ever seeing an ad. Inserting an ad in my Twitter stream would be like inserting ads into (not around) my email. Just don’t do it.