From the press release:
The Kindle Development Kit enables developers to build active content that leverages Kindle's unique combination of seamless and invisible 3G wireless delivery over Amazon Whispernet, high-resolution electronic paper display that looks and reads like real paper, and long battery life of seven days with wireless activated. For example, Handmark is building an active Zagat guide featuring their trusted ratings, reviews and more for restaurants in cities around the world, and Sonic Boom is building word games and puzzles.
Additionally, the revenue sharing was announced, "User revenue will be split 70% to the developer and 30% to Amazon net of delivery fees of $0.15 / MB. Remember that unlike smart phones, the Kindle user does not pay a monthly wireless fee or enter into an annual wireless contract."