Google has announced it will be using (some) microformats and RDFa to enrich search results. They call this Rich Snippets.
To display Rich Snippets, Google looks for markup formats (microformats and RDFa) that you can easily add to your own web pages. In most cases, it's as quick as wrapping the existing data on your web pages with some additional tags.
Official Google Webmaster Blog - Introducing Rich Snippets - May 12, 2009
O'Reilly Radar says
Moving toward the Semantic Web will allow our searching technologies to become more intelligent and will set the stage for the next revolution in which computing systems can become more aware of the "meaningfulness of data".
We've already seen a shift toward "semantic search": Google has already been augmenting search results with Google Maps, limited catalog searches, and more recent entries into the search market such as Amazon's A9 and the yet to be released Wolfram Alpha differentiate themselves by the structured data and content that can be extracted from a search result. We have yet to a see a compelling reason for web masters to place RDFa or microformats into a site to enable this semantic data to be mined until today, until Google provided a social incentive for site designers.
O'Reilly Radar - Google Announces Support for Microformats and RDFa - May 12, 2009
Google has a help file to get you started: Marking up structured data.
Incidentally, if you're thinking, "why didn't someone tell me this structured data thing was coming?" I should mention that actually I did try to tell people, whether it was in my presentation to Allen Press in 2007 (where I talked about the need for microformats and semantic enrichment) or in my keynote to NISO Discovery last year (where I talked specifically about Yahoo SearchMonkey using semantic information).
September 8, 2008 semantic search thoughts