Just my own personal observation.
I receive less payback each month, despite a similar, or higher level of activity.
In fact, this month I made a concerted effort to increase my activity significantly to try and offset a month of holiday, I was very active in Feedback pointing out bugs and so on with the new forum, I also had a Labs Idea implemented and still ...
My Payback is significantly lower nowadays than in my first year of membership.
Of course, without seeing the methodology behind the calculations I can only talk about my impression, but it seems that greater or equal activity is no longer rewarded as highly as before ....
Am I alone in finding this?
Oh, and to clarify, I'm not talking about Payback for SIM activations, I'm only talking about forum activity.