I'd like to point out that even though not every website accepts unicode characters on registration, some software such as vBulletin let the administrator/user

I'd like to point out that even though not every website accepts unicode characters on registration, some software such as vBulletin let the administrator/user to replace the username with such characters once the user is signed up. You may not create as much havoc as in the original post, but some level of confusion at least.