I want to move to Symfony2, because I am totally impressed by its modernity and good programming.
Now I am taking a users table from my old system, with 10,000 users
It is very easy to do with FOSUserBundle. This is the code for it:
$userManager = $this->get('fos_user.user_manager');
foreach ($items as $item) {
$newItem = $userManager->createUser();
//$newItem->setId($item->getObjId());
// FOSUserBundle required fields
$newItem->setUsername($item->getUsername());
$newItem->setEmail($item->getEmail());
$newItem->setPlainPassword($item->getPassword()); // get original password
$newItem->setEnabled(true);
$userManager->updateUser($newItem, true);
}