(disclaimer: I know nothing about MakeMaker)

Generally speaking, i would advise against multiple developers working on the same copy of a (set of) file(s).

It's almost allways worth it to use version control, and have each person check out their own copy of the files.

I would guess that MakeMaker doesn't worry about the leaving files world writable for that reason: It creates files for the current user, which are writable by the current user. Other users should go get their own copy to play with.