Kendall points out "LAMP" hackers not taking RDF to heart as of yet. This might be the case since they tend to use tech only when they need it.. I have noticed that in the last few weeks, the perl CPAN people have been working on their RDF mechanisms for packages - RDF was on the list of solutions for a descriptive web problem that they wanted to solve.
Anyway, most of the article is about rules for the semantic web. Not my area; personally I think we need a LOT more data first. I have heard that RuleML is probably the worst XML syntax ever.