Google now gives webmasters the option to add a simple meta tag to their webpages to tell the search engine not to display their ODP (Open Directory Project) information:

Insert the following anywhere between the header tags:

<meta NAME="GOOGLEBOT" CONTENT="NOODP"></meta>

This news came fresh straight from the bakery, so not every search engine who uses the ODP will immediately follow suit. But here’s the code that applies to all search engines:

<meta NAME="ROBOTS" CONTENT="NOODP"></meta>

Being an ODP editor myself, about 90% of the site descriptions contained in the ODP is outdated. So displaying them within search results subtracts relevance for the end-user off the bat.

From the Inside Google Sitemaps blog.