I guess it doesn't hurt to have it, especially if you're writing a lot of singletons, but it just seems strange to me to do it explicitly since singletons are extremely easy to implement in prototype-based languages.

  singleton = Object()
  singleton.x = 0
  singleton.foo = function(){
      return x + 1
  }

Edit: Also, why not http://www.prototypejs.org/ ? Not that there's anything wrong with playing around with stuff of course.