You might be interested in my thread here: http://www.cgtalk.com/showthread.php?s=&threadid=80278
I started it after going through the 3D World tutorial you are talking about. The problem with the tutorial, is that you always used rounded extrusions (for example, you extruded the leg sockets, which were round, and the ridges on the top and bottom, which were rounded off). In other objects, you might have a curved surface, and then want to pull a hard edges panel out of it or something with hard edges… like a square or something. Anywho, so I posted some questions about this and have been getting good feedback. The dummy object I’m using is the 3x3x3 segmented box you start with in the 3D World Magazine…
It’s taken me a while to grasp the concept of control edges, but I’m slowly getting there. This thread might help since we both are jumping from the same tutorial.
3DZ posted an animated gif earlier in this theory thread that demonstrated adding in control edges. Very cool.