I would hope,that if a free member could accrue more credits than needed for each mailing, that the free member could trade excess credits for banners or text ads. To me the sweet spot would be amount of credits per email in proportion to amount of members. I would rather earn one credit in a new site of 250 members as opposed to 10 credits in a membership of 25,000. If the click through on the little site is 7% and the click through on the big site is 0.07%, I get the same amount of clicks both places but who has time to click 2500 emails for one mailing?Sweet Spot to me would be enough credits to mail every 2 days to a site with a decent click through%