The product I make deals with passwords. We’ve had several bugs over the years that came down to Unicode usernames and passwords containing unexpected characters. Solving them was simple, we just had to be sure to get the encoding and character sets right, but as an American it was eye opening to find so many people with the Euro symbol in password strings.

Related, a friend of mine uses a long list of heavy metal band names as one of his unit tests for strings. Says it catches a lot of weird encoding bugs.

Well aware, just don’t use them in passwords.