nice little anim this buddy... good stuff.
Echoing Adarias slightly - whilst I agree there is a little too much snap - I think it's a great example of how animations don't have to be smooth and continuous in order to work. I'm not sure if this is by accident or by design, if the former then I suggest you read the book I refer to in my sig... if the latter then there's no need as you obviously understand.
One thing I will point out is the hair. You're brave attempting to animate each section, and I'd be inclined to keep the pony tail/bunch as this would be a nice touch. However a number of points I should mention.
1. I looks like you've got the sequence out of synch by 1 frame with the hair mass...? or you could try on the returns (frame 4 to 5 and frame 8 to 1) keeping the hair mass high, and not moving down until the body mass pushes back up again... the secondary motion is failing here. On it's own away from the up and down bob it animates well, it's just when you position it onto the main head shape it fails. Remember with secondary motion you TRAIL the main movement by a frame or 2 - this applies to lose clothing, hair, and so on...
2. The Bunch/Pony Tail (if you keep it) needs addressing - the way you have it moving at the moment looks like it's rotating, it's too stiff... you need to loosen it up by applying the secondary motion techniques I'm referring to.
With this kind of movement you want to be trying to draw S shapes, and then the follow through shapes track along the same paths that you've just made, and then SNAP the movement by inverting the Curve...
I've done a rushed edit to illustrate this...

It's not perfect by any stretch but hopefully it illustrates what I'm trying to get at?
[edit] as a final note, having thought about it a bit further, you're using 8 frames for the run, so you may as well take advantage of that and rather than doing (what is essentially) a 4 frame loop for the hair bounce, use the 8 frames to enhance the hair further... I'd be inclined to swing it from right to left opposite to the rotation of the shoulders...

Keep on Pushin!