1) Firehose! No details yet (coming early 2010), but everyone will be getting full access to the data stream. This is pretty significant news.
2) New home for developers: new website launching within the next few weeks, including status dashboard, tutorials, and much more.
3) Anyone making OAuth requests to Twitter is soon getting an increased rate limit (10x) – about to launch API for browser-less apps, and starting Basic Auth decprecation in June 2010.
4) Twitter is hosting an official developer conference called Chirp in San Francisco next year.