Devel::DProf and dprofpp are perhaps one of the nicer things about developing performance critical applications in Perl. Other languages really don't seem to come close to the ease with which I can use this tool to locate performance bottlenecks and kill them. I often find myself seeing a particular test that runs slowly, but I know I can just type:
$ perl -Mblib -d:DProf t/slowtest.t
$ dprofpp -O 50
and soon all will be revealed. Kudos to the author (I believe it was Ilya, but it's not in the man pages).