Great plugin. I had a Facebook user register/login and her username, which had an ñ in it. I tried your plugin for Username special characters and it did not resolve the issue. Another one had an apostrophe ('). These persons profiles are available via their UID# but not in the url with the special character in the permalink.... e.g. domain.com/profile/fariña
I can resolve this in the backend by removing the characters but in a large network would be hard to track them all down.