Support for PostgreSQL's LISTEN/NOTIFY in PDO has been written since PHP 5.1, it just needs to be integrated with the latest code by one of the core developers - see:

http://netevil.org/blog/2006/oct/background-batch-workflow-processing-with-pdo-pgsql

Following a post on php-dev and a catch-up with Lukas K. Smith, here's an updated patch for PHP 5.3 HEAD that mimics the behaviour of David/Wez's patch, that unfortunately was lost:

http://www.beccati.com/misc/pdo_pgsql_getnotify_php5_3.patch

The patch adds two methods:

int PDO::pgsqlGetPid()

Returns the PID of the connected backend

mixed PDO::pgsqlGetNotify( [ $result_type = PDO::FETCH_USE_DEFAULT [, [int $ms_timeout = 0 ]])

Returns an array or false, just like pg_get_notify()

$result_type can either be:
  - PDO::FETCH_USE_DEFAULT
  - PDO::FETCH_BOTH
  - PDO::FETCH_NUM
  - PDO::FETCH_ASSOC

$ms_timeout is the timeout in milliseconds that the function will wait before returning if no NOTIFY was received

Thanks go to:
Lukas Kahwe Smith for the support
Wez Fufrlong for the feedback and suggestions
David Begley who is the author of a similar patch