Consider a hash of arrays of arrays (HoAoA), where the keys are the urls and the associated value is a reference to an array of arrays:

use strict;
use warnings;
use Data::Dumper;

my %hash;

while (<DATA>) {
    chomp;
    my ( $url, $subject, $date ) = split /\t/;
    $hash{$url}->[0] //= $subject;
    push @{ $hash{$url}[1] }, $date;
}

local $" = ', ';
print "Url|Title|Date(s)|Count\n";
for my $key ( keys %hash ) {
    print "$key|$hash{$key}->[0]|@{ $hash{$key}[1] }|"
      . scalar @{ $hash{$key}[1] } . "\n";
}

print "\n", Dumper \%hash;

__DATA__
http://www.perl.com    Perl    01/05/10 7:44PM
http://www.google.com/page?id=blah    Google Search results for blah  
+  01/05/10 7:44PM
http://www.google.com/page?id=blah    Google Search results for blah  
+  05/10/12 8:12AM
http://www.perl.com    Perl    01/05/10 7:42AM
http://www.perl.com    Perl    01/10/10 9:44PMM
[download]

Output:

Url|Title|Date(s)|Count
http://www.google.com/page?id=blah|Google Search results for blah|01/0
+5/10 7:44PM, 05/10/12 8:12AM|2
http://www.perl.com|Perl|01/05/10 7:44PM, 01/05/10 7:42AM, 01/10/10 9:
+44PM|3

$VAR1 = {
          'http://www.google.com/page?id=blah' => [
                                                    'Google Search res
+ults for blah',
                                                    [
                                                      '01/05/10 7:44PM
+',
                                                      '05/10/12 8:12AM
+'
                                                    ]
                                                  ],
          'http://www.perl.com' => [
                                     'Perl',
                                     [
                                       '01/05/10 7:44PM',
                                       '01/05/10 7:42AM',
                                       '01/10/10 9:44PM'
                                     ]
                                   ]
        };
[download]