This is a three parter. . . a trilogy if you will (I love it when people say, "if you will"), about the basics of setting up an IK/FK snapping script that will correctly position your IK control and pole vector based on the rotations of your FK arm. A little bit of math, some elbow grease and a winning attitude are you need! And some python scripting. And some secret nodes. And a bunch of other stuff too. . .
Part 1 - covers the basics of what it is, why we'd bother and some basics of vector math that we'll need.
Part 2 - covers the hows and whys of writing the basic version of the python script.
Part 3 - covers using funky, cool message attributes to enhance the functionality of the script, etc.