I just received a follow-up email from G, reminding me that I can place more ads on my site:
Subject:
Reminder: There's space for more AdSense earnings on www...
Body:
Did you know that you can place up to 3 content units on each page?
Hi,
We've noticed that you're running less than three ad units on 102 of your pages on <MY SITE>. We recommend that you add any of our top performing units (336x280, 300x250, 728x90 or 160x600) to prominent sections of your pages currently showing only 1 or 2 ads in the placements our heat map suggests.
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Are they getting desperate?
"...to prominent sections of your pages currently showing only 1 or 2 ads in the placements our heat map suggests"
I think ONE to TWO ads in PROMINENT sections of my pages is MORE THAN ENOUGH.