The result of the push pull would in my mind depend on the geometry / face it was derived from, like a flat surface makes a perpendicular extrusion or indentation, a curved however would make a perpendicular extrusion like an outline in 2d of a curved surface. As a reference have a look at the joint push pull tool in SU.

http://forums.sketchucation.com/viewtopic.php?t=6708

Raven