It also appears as if YAML::Syck does this very well:
perl -MJSON::Syck -MURI -E'say JSON::Syck::Dump( bless { foo =>
URI->new("http://www.evancarrol.com") } )'
--
Evan Carroll - me at evancarroll.com
System Lord of the Internets
web: http://www.evancarroll.com
ph: 281.901.0011