You should always provide a great default solution and let the user customize it if he wants to. Once there is ANY user customization, the entire user experience changes. If you want the UX to be ALWAYS the same, you can't let people change stuff.
The problem is, this is contrary to everything done before. I for instance, use Growl on OSX and customized it to my needs. The UX is the best one for me! It's not because Growl devs predicted that. They just let me CHOOSE after providing a great UX already by default.