With Yahoo! getting into the game, it's a good time to be in contextual ad publishing. And it's a particularly good time for AdSense publishers, as the changes Google made to the system this week support better revenue and better tracking of results. The three most important chasnges are:

• Section Targeting. This remarkable addition to the AdSense code tools allows publishers to specify blocks of text to be weighted more heavily by Google's spider when the page is crawled. In using this tool, publishers can fine-tune ad relevancy to the portion of the page where ads appear. It's important to specify a large enough chunk of text to yield meaningful crawl results, lest Googlebot be stumped and PSAs delivered instead of ads reflecting whole-page content. But from an SEO viewpoint, Section Targeting can largely replace global keyword density principles; just get the keywords into the targeted portion of the page.

• 200 channels. The more the better. I'd like to see unlimited channels, frankly, as long as Google limits each AdSense user to one account.

• AdSense for Search Top Queries report. Google now reports the top 25 queries in AdSense for Search, which can spotlight content that site visitors want to see, but might not find. It's a source of new keyword and content ideas.

Changes to AdSense usually come bundled with rewritten portions of the TOS that sometimes have nothing to do with the toolset changes; such is the case this week. JenSense has an excellent before-and-after rundown.