http://wiki.blender.org/index.php/Doc:Tutorials/Animation/Armatures/BSoD/

Mid-point
    SHIFT-snap cursor to 2 points and it will go to the mid-point.

Hot keys
    SHIFT-I IK constrain
    CTRL-I  Assign IK solver cons. to active, targeting other selected
    CTRL-ALT-C  Assign cons. to active, targeting other selected
    You select the targets, then select the depender and act.

IK effector = location defines target of an IK chain

They recommend the following general bone structure
    COG non-deform
        Body non-deform
            Hip deform where all others hang
        *IK  IK effector bones