I would like to suggest

1. Add stackapps.com to list of sites
2. Allow the common "upside-down" unicode characters that have become trendy lately (and some users are using in their names now).
3. Allow basic greek alphabet, since that also seems popular (lot of math and science symbols are greek)

Diff format, tested and working for me in Chrome:

    --- 68252.user.js.orig	2011-08-13 11:15:22.000000000 -0700
    +++ 68252.user.js	2011-08-13 11:51:49.000000000 -0700
    @@ -15,6 +15,7 @@
     // @include        http://meta.answers.onstartups.com/*
     // @include        http://mathoverflow.net/*
     // @include        http://area51.stackexchange.com/proposals/*
    +// @include        http://stackapps.com/*
     // @author         Benjamin Dumke
     // ==/UserScript==
     
    @@ -82,7 +83,13 @@
                                 ,'\u00e0','\u00e1','\u00e2','\u00e3','\u00e4','\u00e5','\u00e6','\u00e7'
                                 ,'\u00e8','\u00e9','\u00ea','\u00eb','\u00ec','\u00ed','\u00ee','\u00ef'
                                 ,'\u00f1','\u00f2','\u00f3','\u00f4','\u00f5','\u00f6'         
    -                            ,'\u00f8','\u00f9','\u00fa','\u00fb','\u00fc','\u00fd'         ,'\u00ff').join('');
    +                            ,'\u00f8','\u00f9','\u00fa','\u00fb','\u00fc','\u00fd'         ,'\u00ff'
    +                            // upside-down lowercase from http://www.fileformat.info/convert/text/upside-down-map.htm
    +                            ,'\u0250','\u0254','\u01dd','\u025f','\u0183','\u0265','\u0131','\u027e'
    +                            ,'\u029e','\u0283','\u026f','\u0279','\u0287','\u028c','\u028d','\u028e'
    +                            // basic greek http://en.wikipedia.org/wiki/Greek_alphabet
    +                            ,'\u0370-\u03FF'
    +                            ).join('');
     
         var bad = new RegExp("[^" + goodletters + "\\w.'-]", "ig");