I like these before-and-after comparisons. This one illustrates a truism about effective Adsense placement – look like navigation, don’t look like banners.
“Recently, Julie experimented with optimizing her link unit ad placement. She removed the existing 120×90 link unit from the uppermost right corner of her pages, and instead placed a 468×15 link unit at the top of her articles. In doing so, Julie found a convenient, unobtrusive location and saw her readers naturally gravitating towards the link unit. Her efforts led to an immediate doubling of her revenue — an increase that has been sustained since the move“