The update includes a variety of optimizations and bug fixes for phones and tablets, as well as a small number of new APIs for developers. The new API level is 15.
The complete list of updates in API’s is as following:
Social stream API in Contacts provider: Applications that use social stream data such as status updates and check-ins can now sync that data with each of the user’s contacts, providing items in a stream along with photos for each. This new API lets apps show users what the people they know are doing or saying, in addition to their photos and contact information.
Calendar provider enhancements. Apps can now add color to events, for easier tracking, and new attendee types and states are now available.
New camera capabilities. Apps can now check and manage video stabilization and use QVGA resolution profiles where needed.
Accessibility refinements. Improved content access for screen readers and new status and error reporting for text-to-speech engines.
Incremental improvements in graphics, database, spell-checking, Bluetooth, and more.
The new platform will be rolled out to phones and tablets in a couple of weeks and should address a number of bugs in the ICS system.
For a complete overview of what’s new in the platform, see the Android 4.0.3 API Overview.