No.
I don't think it's "okay" for developers to release an application for gracias and then charge if it takes off.
Thats worse than selling the app from day one.
It's curious that he just got Angel Funding, and is now pondering how to make money out of it - go figure?
I would pay for increased Twitter API access though, thats for sure.
I'm never opposed to paying for a service or product that I truly benefit from or have a real joy using, TweetDeck being one of them. I pay for Last.fm subscriber status, and it quickly pays for itself in worth.
However, what I think the web needs to realize, specifically those who want to put their goods out there is how to weigh in the expectations of people using your software if it's something built for convenience; there are twitter applications out there by the dozens, $10/year while yes incredibly cheap I don't think is realistic or fair. Some people barely keep up with their twitter accounts for a week, much less an entire year.
Paying for goods and services: yay. Poor payment implementation: nay.