Yahoo is introducing a 'robots-nocontent' tag to help you better identify the different aspects of your site and direct visitors to the sections they're looking for.
With the 'robots-nocontent' tag, the Yahoo crawler is allowed to focus on the main content of your page and target the right pages on your site for specific information they're seeking. In other words, ignore stuff like navigation, headers, footers and legal disclaimers - everything that's not related to the main content of the page. This increases traffic as well as the conversion on your site, and improves the abstracts of your pages in results by removing irrelevant context from search result summaries. It's important to note that this is not a cloaking technique, as all the pages' content is available, and it doesn't change the content that visitors see.
None of the other search engines are supporting the tag yet, so adoption will probably be slow for fear that webmasters mess up their Google rankings.