I think I know where you are coming from with the meta-keywords comparison. The reason why the use of metadata in HTML can fail is that it is often hidden from view. The meta-keywords are out of sight and because of that errors go unnoticed. Microformats don’t have the same problem as most of the data values are in clear sight.
If I am honest I would say that building the semantic web is taking a lot longer than most would hope. There are real points of traction starting to shine through; “Google’s parsing of Microformats/RDFa”:http://googlewebmastercentral.blogspot.com/2009/05/introducing-rich-snippets.html in its search results being the most obvious example. I also hoped the demos with this article would go some way to showing that designers /developers can practically use semantic data today. It may not yet be the grandiose vision, but it’s not a dodo.