Using PDO you have to use a DSN-String to [http://de2.php.net/pdo-construct connect] to the database:

<code type="php">
$dsn = 'mysql:dbname=testdb;host=127.0.0.1';
$user = 'dbuser';
$password = 'dbpass';
$dbh = new PDO($dsn, $user, $password);

</code>

But that's not nice if you have to parse config files for example. It would be nice to config DB-settings using an array as [http://pear.php.net/manual/en/package.database.db.intro-connect.php PEAR::DB], or parameters as [http://phplens.com/lens/adodb/docs-adodb.htm#connect ADOdb]..., too!

PEAR::DB style:
<code type="php">
$dsn = array(
    'phptype'  => 'mysql',
    'hostspec' => '127.0.0.1',
    'database' => 'testdb'
);
$user = 'dbuser';
$password = 'dbpass';
$dbh = new PDO($dsn, $user, $password);
</code>

Furthermore it would be very beneficial to also support the PEAR DSN format since its well established and documented:
http://pear.php.net/manual/en/package.database.db.intro-dsn.php