Currently, Extrapolation mode is in the Key menu (Key->Extrapolation) of the Graph Editor, indicating that it works if you select a control point in the Graph Editor. This is not the case. In order for you to properly set the extrapolation mode, you have to first select the channel from the Channel region on the side of the Graph Editor. This means that the menu item should probably live at Channel->Extrapolation instead of its current home. In addition, it would be nice if the Shift+E hotkey worked from within the Channel region of the Graph Editor as well as the graph part of the Graph Editor (currently the hotkey only works in the graph section).