The following changes were made at version 3.1:
Attribution Widget added to the API to show information about the data sources used to build the map services displayed in the map. The screen shots below show the default version of the widget and the expanded version of the widget (the widget expands/collapses with a single click):
The widget automatically updates based on layer visibility and map extent. Attribution is automatically included when using the full build of the API. When using the compact build, it must be manually included. See the Attribution Widget API reference for more information, including the CSS classes used to change the look of the widget.
Additions and changes to the esri.Map class:
Additions to the esri.layers.Layer class. All layers now have minScale and maxScale properties as well as methods to determine if a layer is visible at a specific scale. All layers now have attribution properties and methods to suspend and resume drawing. The Layer class documentation has more information.
The Overview Map now has public show and hide methods.