From the command line:

echo Just another Perl Hacker | perl -pe lc

16 unique Characters. Assuming (from one of your later posts, that this is your general algorithm:

my $string = q{echo Just another Perl Hacker | perl -pe lc};

$string =~ s/\s+//g;

$string = lc $string;

my %chars;

map { $chars{$_} = '' } split //, $string;

print scalar keys %chars;

What do I win? ;-)