I'd heard rumours about Google cutting earnings just before payment was due but always thought it was folklore or people not reading stats right.
But I have had my Adsense admin area saying over $900 was due for my next payment. Today, it says just over $200 is due.
Normally, if it is because of invalid clicks, this is listed in the payment area and is often a few dollars at most. There is no mention of the reason for this huge drop, and the only answer I can get is that "inflated earnings readjusted" template response they give.
What happens to that missing $700? They say it goes back to the advertiser, but as an advertiser spending $$$$s on Adwords for other sites I own, I've never, ever, ever received credits back.