Semantic HTML makes it easier for Google to crawl and 'understand' a website but what about microformats? Are microformats any more semantic/crawlable then standard HTML markup?
Google announced a little bit of RDFa and Microformats support in the last few days.
Links and commentary here:
http://rdfa.info/2009/05/12/google-announces-support-for-rdfa/
Yahoo has been using RDFa and Microformats to drive Search Monkey for some time:
http://developer.yahoo.com/searchmonkey/
Both will probably aid click-through rates, but not necessarily ranking. Expect more search engines to use more different RDFa vocabularies as time goes on. BOSS is also relevant here:
http://developer.yahoo.com/search/boss/
The intent is to help create more search engines and they will have access to the data in the pages.