I just published a response to a blog query about twitter, and I'm happy enough about it I thought I'd post it here (just so I'm sure to get credit :-)
Twitter may not be for every business, or maybe not any, but it could still play a significant social and financial role. The non-friend entities I follow on twitter are mostly scientifically-oriented news organizations & politicians. Both sorts of individual pay for advertisement. I also have feeds from small local arts theatres. You don\’t have to be challenging M$ in order to have a viable business model. Twitter really could be one of the things just replacing newspapers.
I think twitter should charge anyone with over 500 followers a little. I think they’d pay. It’s like adsense, you *know* how many people are reading what you put out, so you know what it’s worth. And it’s only worth a little. But to many, many people.