Are you using Google Search Box or planning to use it on your website or blog. If yes, then you must read this post. Google Search adds you extra income from Google Adsense. But before adding it on your site, you must at least once go with Adsense Policies of Google. I have seen many blogs which do implement the Google search code on their sites, violating the Google policies.
As per Adsense policies for Google-Search,

AdSense for search: A maximum of two Google AdSense for search boxes may be placed per page. Also, a single link unit or a search box, but no other Google ads, may be placed on pages with AdSense for search results.

You can read this here at Google Adsense Policies

So, if you are using Google Search on your blog, be sure that search results page do not contain any other ads except the search-ads. However, you can place a single link unit, but I do prefer not to use any other ads. People do generally forget about header ads. They do make separate page for search results but if their header contains Adsense or any other ads, those ads are still being shown along with Search-Ads.

If you too have made this mistake, correct it now before Google sees you.