(
  siteA => ('10-9-11' => 3,
            '11-9-11' => 1,
            '12-9-11' => 2),
  siteB => ('04-04-11' =>5,
            '05-05-11' =>1)
)

##</code><code>##

my %h;
# New site
$h{'siteA'} = {'09-10-2011' => 1};

# Second instance of site and date found, increment.
$a{'siteA'}->{'09-10-2011'}++;

# Another date found for siteA, '10-10-2011'
...