Why is Twitter so popular, even though few know how to use it?

The more time I spend on Twitter, the more I see it dominated by four groups of people. CEOs of large corporations, celebrities, online marketers looking to promote their small businesses and news media types. When I talk to these people, or others, about Twitter, few really seem to know why they are there or what they're doing. It seems that Twitter is a new tool for which we don't yet have a defined need or purpose, but we're committed to using it anyway.

For me this begs the question, who is driving this commitment, users who are convinced of its coolness or effectiveness or some genius marketing type at Twitter? Either way, its popularity is growing, even if no one can explain why. I guess this is the part where I confess to having been on Twitter for more than a year now (but only for research purposes only, of course). See my experiment at http://twitter.com/phillipbarnes.