Knife tool doesn't cut obscured edges I'm using Blender 2.66,  I find that the knife tool (K) doesn't work the way it used to.  


Dragging across an obscured edge, even if selected, doesn't cut it.
There seems to be no way to activate the option to do a midpoint cut or multiple cuts.
Knife will cut through obscuring faces, if Z is pressed while cutting, either on solid or wireframe mode. 

Midpoint snap can be activated by pressing Ctrl while cutting.

Further options are displayed on the 3D View area's header, while Knife tool is active.