We initially thought the fees for using the Google AdWords API would begin July 1st but that didn't happen. New reports via WebmasterWorld say Google has sent out emails to AdWords API users that the fees are to begin this October 1st.
I received notice today that there is a transition in September to this new system ($.25 per 1000 quota units) and charging will begin Oct 1.
For one advertiser who uses 30M calls, it will cost each month $7,500 in additional expenses.
Now it is still unclear to me if this fee will be charged to everyone including advertisers, tool aggregators and agencies. I am sure there will be discounts made available to some.
Forum discussion at WebmasterWorld.