Interesting, because I don't actually pay that much attention to the karma stuff - and my impression is that it's really not the most essential part of the philosophy, either. The part of 'karma' that I buy is that what we do creates 'tendencies' for us to keep doing that. Psychological 'grooves' if you will. And unless and until we are willing to look at those, and make choices to act in different ways, we keep running in those 'grooves'.

I don't pay attention to the 'how you got born into this place and time' parts because, to me, that's really irrelevant. You can't control that, and you don't have any way to know if you did or did not 'choose' it metaphysically. What you -can- control is how you respond, how you grow, and what you choose to do now that you're here. And that to me is far more important than how you got there.