As far as use warnings; goes, I normally remove it from non-critical production code that I don't actively use. I'll leave use strict; in forever, but I remove use warnings; because it can cause warning messages to pop up in perfectly valid code when versions of Perl change (and definations of what is warnable change with it). It makes users nervous, and normally doesn't affect much.

I picked this practice up from Learning Perl, 3rd ed. The passage I took it from:

"Of course, warnings are generally meant for programmers, not for end-users. If the warning won't be seen by a programmer, it probably won't do any good. And warnings won't change the behavior of your program, except that now it will emit gripes once in a while. If you get a warning message you don't understand, look for its explanation in the perldiag manpage.

Warnings change from one version of Perl to the next. This may mean that your well-tuned program runs silently when warnings are on today, but not when it's used with a newer (or older) version of Perl. ... But you shouldn't count on the text or behavior of any warning staying exactly the same in future Perl releases. "