As long as I've been doing WordPress themes, I never thought about this. I know you can make a template file for an error 404 page (404.php), and prettify it in your WordPress theme - but can you do it for 500? 503? 400? 401?
Someone just asked me this and I've never thought about it. Is it possible? Or does the 404.php file cover all of them? (or do you have to just use your server to add these other ones, and can't do it through WordPress?)