No mention of this in "What's New".
In past releases grids and levels cared whether you sketched them "right to left" or "left to right". What? Okay...when you drag a grid or level to change its extents Revit will drag all the other grids or levels along with it automatically as long as they have the same "head" and "tail" orientation.
In 9.1 they don't anymore. They align and behave together regardless of which way you sketched them. Thanks!! I like it!!