Functions to add to wp-members-pluggable.php to create a situation where you log in to Wordpress using email address instead of username.

wp-members-pluggable.php

<?php
/**
 * WP-Members Pluggable Functions
 *
 * These functions replace those in the wp-members plugin
 *
 */

add_filter( 'wpmem_inc_login_args', 'wpmem_inc_login_args_filter' );
if ( ! function_exists( 'wpmem_inc_login_args_filter' ) ):
	/**
 * Filter login form to change legend
 *
 */
function wpmem_inc_login_args_filter( $args )
{
	
	return array( 
		'heading'      => __( 'Sign In', 'wp-members' ));
}
endif;



add_filter( 'wpmem_inc_login_inputs', 'wpmem_inc_login_inputs_filter' );
if ( ! function_exists( 'wpmem_inc_login_inputs_filter' ) ):
	/**
 * Filter login form to change username label
 *
 */
function wpmem_inc_login_inputs_filter( $default_inputs )
{
	$default_inputs[0]['name']= __( 'Email', 'wp-members' );
	return $default_inputs;
}
endif;




add_filter( 'wpmem_inc_resetpassword_inputs', 'wpmem_resetpassword_form_filter' );
if ( ! function_exists( 'wpmem_resetpassword_form_filter' ) ):
	/**
 * Filter reset password form to show only a text box requesting email
 *
 */
function wpmem_resetpassword_form_filter( $defaults )
{
	
	return array(
			array( 
				'name'   => __('Email Address', 'wp-members'), 
				'type'   => 'text', 
				'tag'    => 'email', 
				'class'  => 'password',
				'div'    => 'div_text'
			)
	);
}
endif;



add_filter( 'wpmem_pwdreset_args', 'wpmem_pwdreset_args_filter' );
if ( ! function_exists( 'wpmem_pwdreset_args_filter' ) ):
	/**
 * Filter password reset form submitted values to set username to the value entered for email address
 *
 */
function wpmem_pwdreset_args_filter( $args )
{
	$args['user']=$args['email'];
	
	return $args;
}
endif;

add_filter('wpmem_register_data','wpmem_create_username_from_email');
if ( ! function_exists( 'wpmem_create_username_from_email' ) ):
/**
 * Create Username from Email
 *
 * Creates a WP-friendly username from email address
 * Address is alreay confirmed valid before filter is called
 * [[[  is_email( $fields['user_email']) in wp-members-register.php/wpmem_registration  ]]]
 *
 * @uses get_user_by
 * @return array Returns filtered registration fields passed in from wp-members-register.php/wpmem_registration
 *
 */
function wpmem_create_username_from_email($fields) {
    $generated_username=sanitize_user($fields['user_email'],true);
    if ($fields['username']=='tempusername') {
        $fields['username']=$generated_username;
        $fields['nickname']=$generated_username;
        $fields['display_name']=$generated_username;
        $fields['user_nicename']=$generated_username;
    }
    return $fields;
}// end create_username_from_email
endif;

add_filter('wpmem_register_form','wpmem_hide_username_registration_field');
if ( ! function_exists( 'wpmem_hide_username_registration_field' ) ):
/**
 * Remove username field from registration form, then create a hidden field
 * with name='username' and set value to 'tempusername' so the form validates
 *
 */
function wpmem_hide_username_registration_field($form){
    // include PHP DOM parser from http://simplehtmldom.sourceforge.net/
    include ('simple_html_dom.php');

    $html = str_get_html($form);
    // remove username label
    $usernamelabel=$html->find('label[for=username]', 0);
    // remove username input field and wrapping div
    //$usernamediv=$html->find('input[name=log]', 0)->parent ()->outertext='';
    $usernamelabel->next_sibling()->outertext='';
    $usernamelabel->outertext='';

    // append hidden field to the <legend> tag (the beginning of the form)
    $legend=$html->find('legend',0);
    $legend->outertext=$legend->outertext.'<input type="hidden" name="log" value="tempusername">';

    $rows=$html->find('div.div_text, div.div_checkbox');
    foreach ($rows as $row)
        $row->outertext=$row->outertext.'<br style="clear:both" />';

    // these changes are optional, removing 'reset form' button and adding Twitter BS3 classes to the submit button
    $clear_button=$html->find('input[name=reset]',0)->outertext='';
    $submit_button=$html->find('input[name=submit]',0)->class='btn btn-primary';

    return $html;
}
endif;

?>