Twitter is the hot thing - but not as hot as YouTube

Check out this growth chart of some of the latest, hottest social media companies

Now one could argue that it's not about unique visitors. It's all about the number of "tweets" whereas YouTube is truly a destination site. Eventually you build a community, then you need to figure out how to make money. Hopefully, Twitter figures it out quicker than Facebook (still searching) and YouTube (still searching too).