if I create a new object, and then go into edit mode and click on "normal transformation orientation" the z axis always runs along the face's normal, but the x and y are all over the place. Sometimes the X faces left, other times it faces down etc. how is this determined, and is there a way to rotate the x/y without rotating the face itself?

A little more info. Blender allows you to go into edit mode, select normal transformation orientation and then rotate around the objects normal (R+Z+Z) you can also rotate around the NORMAL'S X and Y axis R+X+X for example and tilt a face backwards and forwards even when it's sitting at a strange angle. This is really useful. Unfortunately, because there is no consistency in which direction the x and y are facing, tilting multiple faces at once will cause some to tilt forward, and others to tilt back and others to tilt off to the side.

If I create a new object, and then go into edit mode and click on "normal transformation orientation", the z axis always runs along the face's normal, but the x and y are all over the place. 

Sometimes the X faces left, other times it faces down etc. How is this determined, and is there a way to rotate the x/y without rotating the face itself?

A little more info. Blender allows you to go into edit mode, select normal transformation orientation and then rotate around the objects normal (R+Z+Z). You can also rotate around the NORMAL'S X and Y axis R+X+X for example, and tilt a face backwards and forwards even when it's sitting at a strange angle. 

This is really useful. Unfortunately, because there is no consistency in which direction the x and y are facing, tilting multiple faces at once will cause some to tilt forward, and others to tilt back and others to tilt off to the side.