You see, I almost exclusively write pure-Perl modules. Thus, the "make" step always consists of making a structure under "blib" that consists mostly of empty directories, copying all my.pms into "blib/lib", and manifying pods into blib/man3.
This is useless for me while developing. I don't actually care about manifying PODs until I'm ready to "make install" anyway. And copying the modules just means that sometimes blib/lib is out of date when I'm running "prove" (or even "make test", if I just made a new module and haven't reran Makefile.PL yet), and more annoyingly they show up in every grep, and have to be ignored by version control, etc.
I suppose part of my annoyance would be fixed by making a shell script that uses "prove -l" to simulate the effect of "make test" using modules from "lib" instead of "blib/lib", and just never run "make" or "make test" while developing. But still. Ugh.