Senh: I think this is a good compromise. The hardcore users will pay for it. Hopefully, that's enough to make up for the lost in print advertising.
So far, I’ve only heard of two people who are willing to pay for Twitter - Guy kawasaki and Roger Ebert. If you search on Google, you’ll probably find more, but those are the only two I’ve read about. They have one thing in common - they each have over 100,000 followers.