Jensense has a post about a new feature in AdSense for Search. Previously, the search results were displayed on a page outside of your site. As a result, visitors were led off of your site. With Google's new feature, the search results can be displayed on your site.
The new feature was not hard to implement. However, I noticed two problems. First, the width of the results page is set at 650. For some sites, especially sites that have side columns, the 650 width is too wide and messes up the layout of the page. I was tempted to change the width, but that would have violated Google's terms about not changing their code.
The other problem I encountered was with WordPress. The Javascript provided by Google works just fine on non-WordPress pages, but do not seem to work on WordPress-powered sites. On the results page, the search box is displayed but there are no search results. At the bottom of the page is an icon indicating a Javascript error. The error message, as usual, was of no help. If you are using WordPress, my recommendation is to test it during a slow period or on a test page your visitors will not see.