Comment Markup (Score 3, Informative) 50
RDF is nice and there are various different syntaxes for it (including various triples formats), and promises, if it can be built, deployed and trusted(!!!) to make the web ever so much more searchable. This will depend though on people writing good ontologies (not easy) and using them correctly (even less easy).
RDFa and microformats look, on the surface at least, to be nice ways to manage RDF type information in HTML. But I'm a bit more dubious - they don't, in many cases, have careful ontologies built around them - when they do (RDFa, mostly) they seem to be very resource intensive (a heavily RDFa annotated HTML page is likely to balloon to several times the same page without RDFa), and the uses of them I've seen have been less than convincingly correct. This doesn't mean that they're useless, just that they're not doing the job at the moment, or they're doing the job poorly.
The solution that seems to be favored by the semantic web types is to present RDF pages as an alternative to HTML pages when RDF is requested. This looks, by far, to be the best way to work this, but does require site builders (and CMSs and web frameworks), and content authors, to be able to build correct RDF pages that represent the information presented, often at the same time as they present HTML pages to human readers (and non-RDF search engines). This is going to be a major problem.