Description:
------------
Currently the DateTime object construction accepts a strtotime type input only for setting the date on the object.  This means that when trying to get the current time WITH microseconds you have to do something like this..

<?php
$t = microtime(true);
$micro = sprintf("%06d",($t - floor($t)) * 1000000);
$d = new DateTime( date('Y-m-d H:i:s.'.$micro,$t) );
?>

which is highly inefficient as we are converting a float into a string and then converting it from a string into the internal format for the DateTime object.

It would be really nice to have a constructor for the DateTime object that would accept a float argument (defaulting to NOW w/ microseconds)

Possible suggestions would be
factory method
$d = DateTime::TimeWithMicroseconds();

make the constructor accept a float
$d = new DateTime(microtime(true));

modify the setTimestamp method in PHP 5.3 to accept a float.
$d = new DateTime();
$d->setTimestamp(microtime(true));