XML::FOAFKnows::FromvCard is a Perl module to create simple foaf:knows records from vCards.
# read a vCard file into $data
my $formatter = XML::FOAFKnows::FromvCard->format($data);
The foafvcard script in the distribution is also a good and more elaborate usage example.
This module takes a vCard string parses it using Text::vCard and attempts to make foaf:knows records from it. It's scope is limited to that, it is not intended to be a full vCard to RDF conversion module, it just wants to make reasonable knows records of your contacts.