Twitter's only recently become an international sensation, but, unlike some of its more slow-and-steady contemporaries, it's already looking to make a buck and this week hinted again at letting the ad revenue stream in. This may not end well.

Though they've always admitted they could possibly, maybe, potentially open the door to advertisers, Twitter founder Biz Stone seemed to chart a more definitive course yesterday afternoon when he tweeted, "We leave the door open for advertising. We'd like to keep our options open, as we've said before.