I've cleaned up the 2006 photos and am in early 2007. I had a different camera then - not nearly so technologically advanced as my current model. For example, it had a fraction of the speed in burst mode, struggling to achieve 3fps where the current camera can comfortably rip 5 or more fps.
But I'm not sure that is the explanation for the observation that I took a lot fewer photos back then. In a day, I now can easily end up with over three or four hundred images in the course of casual shooting. In 2007, it looks like a big day was about 40.
I don't know if my keep rate has improved, but I am certainly better at pressing the clicky button more often.