That's right, from the Google AdSense: What's New page:
To provide even more value to your users, and to help you further monetize your web pages, we're allowing publishers to place up to three ad units on every web page. Our system will automatically recognize the additional ad units, and will serve unique ads to each. Your ad units can each have different color palettes, formats, and alternate ad URLs, providing you with the flexibility you need to incorporate Google ads into your site design. Please read the Multiple Ad Units section of our FAQ for the full details.
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