The unified version of Android, for tablets and mobile phones alike, was officially announced and its SDK is already available for developers.

The big highlight for this version is the unification of Android 2.x and Android 3.x, which simplifies the development and design of apps. 

New mentionable features in Android 4.0:

• Social API. Demonstrated through the new People app showed in the presentation. Android now provides a hub for you contact's social activities and not just a name-phone table of data.
• Android Beam. NFC based, allows you to share information or establish a connection with another phone, by physically connecting them.
• Find more on the Android developers site. 

You can also check out the whole presentation on Android 4.0 and the new Galaxy Nexus here.