As I have been using Revit 2013 I have noticed what I like to consider a bug, or at least a change in work-flow since the last release.  Maybe I consider it a bug because I don’t like the new work-flow so don’t be jaded by my opinion.  When orbiting a model in 3D it will pick the center of the model as a pivot point, unless you select an element, this then becomes the pivot point, this is the same as previous releases.  However if you unselect that element it still remains the pivot point for that veiw (new to Revit 2013, similar to Navisworks) and to reset this you must either close the view or click on the veiw cube to reset it back to the center of the model.  I don’t know if this was by design or accident but if it could be set back to the old way this would be nice.