Globalization is a serious issue if you create a software that is to be used worldwide. You may for example take into account that people have non a-z letters in their names, like for example ‘ź’. If you don’t consider that, your users may come across windows like this one, I saw while registering to Windows Live Spaces.
So what should I do? Lie about my last name? And the funniest thing is: there’s no ‘ź’ on the list of forbidden characters.