Slick! I wouldn't have thought of using reduce for this. I'll ++ you tomorrow when I get more votes ;)

There is a small bug in the implementation, though: single number ranges fail. Add 618 or 619 to the test data, you get "618 isn't there!".

Here's a patch to fix it:

# $last ||= 1; # needs to be
$last ||= $first;
[download]

And here's another patch that disposes of pre-allocating the 1000 character string for $zones. I'm sure it's slower, but it'll work for an arbitrary range (ie, > 1000):

my $zones = reduce {
    my( $first, $last ) = split '-', $b;
    $last ||= $first;
    
    #allocate $a here
    $a .= chr(0) x ( $last );
    
    substr( $a, $first, $last - $first + 1 ) = 'x' x ( $last - $first 
++ 1 );
    $a
} '', split ',', 
'10-374,376-379,382-385,388-499,530-534,541-543,618,619,700-704,707-70
+9';
[download]

Update: added second patch