RDF-Trine (and companion RDF-Query) is *the* toolkit to use if you want to do any RDF or Semantic Web programming in Perl. It is the foundation which most other Perl RDF tools (RDF-Endpoint, RDF-LinkedData, Test-RDF, etc) build upon.
This seems to be the best Perl module available for processing RDF. It has a nicely designed API and it works very well. There is an associated SPARQL query engine (RDF::Query), which also works really well.
I have found (and submitted) a few bugs, but they have all been relatively minor.