ken_b - 10:06 pm on May 8, 2010 (gmt 0)
From Googles "Interest-based advertising: How it works" [google.com]
Notice that it doesn't mention anything but visiting sites that use AdSense, no mention of any other "interaction".
Mary's favorite hobby is gardening. With Google's interest-based advertising technology, Mary will see more relevant gardening ads because she visits many gardening websites. Here's how that works:
1. When Mary visits websites that display ads provided by Google's AdSense program, Google stores a number in her browser (using a "cookie") to remember her visits. That number could look like this: 114411.
2. Because many of the websites that Mary visits are related to gardening, Google puts her number (114411) in the "gardening enthusiast" interest category.
3. As a result, Google will show more gardening ads to Mary (based on her browser) as she browses websites that use AdSense.