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?
As far as i know Google doesn't actively talk about these micro formats as a way of generating your page rank, from what i understand its more for other kinds of bots that are not just making a general purpose search engine.
For geographical information, Google will parse KML files and index them and the links in them.
I believe that Yahoo has gotten behind RDFa I don't think that Google has admitted to this yet.
At the moment Google did not announce any support for microformats yet. I hope, that in the near future they will.
On the other hand Yahoo has announced that it will support RDFa, eRDF and microformats.
AFAIK, all major search engines support the rel-nofollow microformat. Beyond that, I'm not aware of any support. However, there are smaller, more specialized search engines that have been specifically designed with microformats in mind. E.g. there are search engines that allow you to do searches on relationships between persons, using the XFN microformat.
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.
They make your pages more semantic insofaras they force a bit more consistency in the way that you fit your information together. The major search engines can and do read microformats, and often use them to display what Google calls "rich snippets" ( http://googlewebmastercentral.blogspot.com/2009/05/introducing-rich-snippets.html ), which adds some interesting stuff to SERPs. Bing and Yahoo both display these too.