Google has gone and released a non-final preview of the official Android 3.0 SDK. This will allow developers to not only test their applications with the upcoming tablet OS, but it allow them to visually integrate their app with the operating system inheriting the new "Holographic" theme.
It's worth noting that applications developed with the 3.0 SDK preview can not be eventually published to the Android Market, but the final SDK will be available in the coming weeks.
With the SDK we learn a few key details about Honeycomb. 3.0 will feature the system bar at the bottom of the screen that will display global status notifications and an action bar at the top of the screen will be available for application control. Honeycomb will also feature 5 customizable home screens. They each feature a large grid which will allow the placement of widgets, applications, and other shortcuts that we are all used to.
The highlights are pretty extensive, so it's recommended for you to check out the official preview over at the Android developer site.