From http://wpsnipp.com/index.php/date/capture-users-last-login-date-and-time/

new_gist_file

function your_last_login($login) {    global $user_ID;    $user = get_userdatabylogin($login);    update_usermeta($user->ID, 'last_login', current_time('mysql'));}add_action('wp_login','your_last_login');function get_last_login($user_id) {    $last_login = get_user_meta($user_id, 'last_login', true);    $date_format = get_option('date_format') . ' ' . get_option('time_format');    $the_last_login = mysql2date($date_format, $last_login, false);    echo $the_last_login;}