astrobiologist - 7:45 am on Nov 4, 2009 (gmt 0)
My site gets close to a million visitors a month at peak, which basically is during the academic year; although I sometimes earn more on low-visitor days. I benefit earnings-wise by a lot of those folk being non-repeats; most of my traffic comes from organic searches. Although the site is science and technology based it covers a lot of topics and has about 14,000 pages of unique, rich, densely cross-linked content. I like to keep my ads mostly in one place -- at the top. That way people get to see the ads first, when, in my experience, they are mostly likely to click on them, and also, they're not being bothered by ads while they're reading the content. I use a medium rectangle and a small ad links unit. I rarely bother to check what ads appear -- they vary enormously from page to page, day to day, place to place (very different for example in the US, UK, and Spain), and even from ad to ad within the same block. I think it's this diversity that helps cushion my earnings from wild fluctuations. I don't get into trying to affect what ads show, keywords, etc. I just concentrate on quality content and let the system do its thing.