gistfile1.php

function np_replace_howdy($wp_admin_bar){

	//New text to replace Howdy
	$new_text = 'Welcome';

	//Call up the 'my-account' menu node for current values.
	$my_account = $wp_admin_bar->get_node('my-account');

	//Replace the 'Howdy' with new text with string replace
	$new_title = str_replace('Howdy', $new_text, $my_account->title);

	//Rebuild the menu using the old node values and the new title.
 	$wp_admin_bar->add_menu(array(
		'id'     => $my_account->id,
		'parent' => $my_account->parent,
		'title'  => $new_title,
		'href'   => $my_account->href,
		'group'   => $my_account->group,
		'meta'   => array(
			'class' => $my_account->meta['class'],
			'title' => $my_account->meta['title'],
		),
	));
  }

add_action('admin_bar_menu', 'np_replace_howdy', 999);