I’m assuming your website has one or more forms on it (if you’re not trying to capture visitors’ details you may as well pack up and go home now) …but have you tried to break those forms? You know the sort of thing – leaving vital information out, entering impossible email addresses, etc. Having a form which doesn’t ensure the right information is entered is like taking someone’s business card and not glancing down to check they haven’t given you their rail ticket instead.
The thought just occurred to me when I read the short post Noticeable Errors on Future Now’s Marketing Optimization Blog. It just shows how a good error message should Look. After all, someone filling in a form on your website actually wants your stuff, so make it as easy as possible for them. Even if they can’t fill in a form correctly.