Just because something is old and there's a new way of doing it doesn't mean that you should abandon the old. For one thing, 'use warnings' won't work on some older perls. If you care about them - and I do - then 'use warnings' is a bad idea.

I do 'use warnings' when developing my code, but I try to remember to remove it when I do a release. I usually forget and am prompted to do so by test failures being reported by the CPAN testers. Quite often those failure reports come from my own testing boxes :-)