I am just digging into Tom Igoe's kick'n book but am running into a little issue.
By happy coincidence I happen to have a copy of his book nearby--well, more due to the local library. 
(It was total luck I found it though, it wasn't catalogued under computers or electronics it was under robotics--in a third, completely separate physical shelf location...)
Neurascenic:~ neurascenic$ /dev/tty.usbserial-A4000PBA 9600
-bash: /dev/tty.usbserial-A4000PBA: Permission denied
You're actually missing something important, but from looking at the text I can see how easily you could.
What you need to type is:
screen /dev/tty.usbserial-A4000PBA 9600
You're missing the actual command you need, in this case screen which--in the book--is printed in a different colour (black--the same colour as the text) to the parameters (purple). I can see how you'd miss it.
The reason you get "Permission denied" is probably because you're telling the computer to try to execute the serial port as a command. (It could also be because you don't have permission to access the port--which may mean you still get the same permission error when you use the correct command.)
Hope this helps...
--Phil.