From Twitter’s new close-down terms of service for their API:
5. (e) You may not use Twitter Content or other data collected from end users of your Client to create or maintain a separate status update or social network database or service
which I interpret as - you can’t write a twitter client and then post anything through that client to any other service. What I think this means is that when you make a twitter client, all it can do is read/write twitter and read from other data sources. This effectively shuts down the development of any differentiated application. I’m not sure that the sweeping ownership statement of ‘other data’ is any way enforceable, but it doesn’t have to be - Twitter runs this here town.
Update: - Yoink! Twitter has yet to shut down my badly-programmed and disrespectful web client that translates your tweets (badly) to a Scottish accent - http://tweiter2.heroku.com/.