One more rigging research. Just a first test of new FK IK switch attitude.
Mainly I have focused to over come all possible dependencies.
It has no jumps of FK and FK controllers, in FK mode IK controllers follow, in IK mode FK ones follow automaticaly.
It is based on separate FK and IK rig. They are connected by external IPO drivers (see cubes in Layer 2). For keying you just have to use Visual keys (I do not know why but Blender has some difficulty to key visual keys in auto key mode).
Old know problem, sometimes you have to go on frame forward and back for update.
Sorry no squash and stretch yet.
I hope that someday someone will find really final and animator friendly solution for FK/IK switch. It seems to me that Nathan`s solution in simple biped rig is maybe most appropriate still when you learn how to use FK IK switch using visual keys.
Looking forward to all comment and improvements.