add_filter( 'gettext', 'wpse17709_gettext', 10, 2 );
function wpse17709_gettext( $custom_translation, $login_texts ) {
// Login Main Page
if ( 'Username' == $login_texts ) { return ''; } // Username Label
if ( 'Password' == $login_texts ) { return ''; } // Password Label
if ( 'Remember Me' == $login_texts ) { return ''; } // Remember Checkbox
if ( 'Log In' == $login_texts ) { return ''; } // Login Button
if ( 'Lost your password?' == $login_texts ) { return ''; } // Lost Password Link
if ( '← Back to %s' == $login_texts ) { return ''; } // Back to website
// Login New Password
if ( 'Please enter your username or email address. You will receive a link to create a new password via email.' == $login_texts ) { return ''; } // Message after logo
if ( 'Username or E-mail:' == $login_texts ) { return ''; } // Label of username input
if ( 'Log in' == $login_texts ) { return ''; } // Log In Link Text
if ( 'Get New Password' == $login_texts ) { return ''; } // Button
// Messages
if ( 'You are now logged out.' == $login_texts ) { return ''; } // Log out message
if ( 'User registration is currently not allowed.' == $login_texts ) { return ''; } // User registration disabled
if ( 'Check your e-mail for the confirmation link.' == $login_texts ) { return ''; } // Check link confirmation on email
if ( 'Check your e-mail for your new password.' == $login_texts ) { return ''; } // Check new password on email
if ( 'Registration complete. Please check your e-mail.' == $login_texts ) { return ''; } // Registration complete
if ( 'Your session has expired. Please log-in again.' == $login_texts ) { return ''; } // Expired Session
if ( '<strong>You have successfully updated WordPress!</strong> Please log back in to experience the awesomeness.' == $login_texts ) { return ''; } // Sucessfully Wordpress Updated
return $translation;
}