Personally, I tend to 'use warnings' unconditionally in my production code, not only in debug mode. If I was too lazy to stamp out all the warnings before going to production, I deserve whatever happens to me. If something later goes wrong, I like to know about it as early as possible. Just my $0.02 worth.

Update: Blush. I didn't try it until now ... but I get a syntax error if I try to use warnings conditionally:

#!/usr/local/bin/perl
my $debug = 1;
use warnings if ($debug == 1);
use Data::Dumper if ($debug == 1);

syntax error at ./test8.pl line 3, near "use warnings if"
Execution of ./test8.pl aborted due to compilation errors.
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