From BlenderWiki
Collapsable Display of Subtracks
Collapsable Action Channels
Action Channels can now be collapsed, to hide Constraint Channels and other subtracks underneath it. Use the arrow beside the name of an Action Channel to do so.
Subtrack Options
When you expand an Action-Channel by clicking on the triangle beside its name, you will now be presented with options to show/hide the ipo-curves represented by the Action-Channel, and/or the Constraint Channels belonging to that Action-Channel.
Actual ipo-curves will not be drawn in the Action-Editor, but the keyframes will be shown.
Renaming Action/Constraint Channels
With the mouse-cursor over an Action Channel or Constraint Channel's name, it is now possible to rename that channel by pressing N, much like doing the same with shapekey-channels. You can also use CtrlLMB 
or CtrlRMB 
to do so.
In the dialog that pops up, you can also change the 'protection' and 'collapsed/expanded' status of that channel.
Other changes worth noting...
ShapeKey Support
In the past, when an Object had ShapeKeys, the ShapeKey channels + sliders would draw on top of Action Channels, cluttering the view. Also, when an Object had ShapeKeys, the action data of the Action in the Action Editor, would not be able to be edited or modified in any way. Now, ShapeKey channels for the active Object will only show if there is no active Action.
