People should be able to customize their software as much as possible. We should be able to change the look of the software, the key bindings, the level of help provided by the applications, everything except the type of functionality that the software provides. The only thing which should be immutable in software is the functionality. Everything else should be changable by a user setting. Emacs does this. So does Vern. A lot of the various MP3 players such as Winamp and Sonique are on their way. Customizability is one of the main reasons that UNIX and X-Windows are better than Windows at getting a personalized user experience.

The big problem with personalizable software is that the personalization is either hard to code, or hard for users to understand. Toolkits which make personalizing software easy for the programmer as well as the user are therefore worthwhile and a Good Thing.