[railsmax]

Prototype, Underscore, jQuery, Coffescript, .... RubyJS - nobody love pure JS, when you've got a chance to write nice code(short and descriptive) - why don't use this ability? And about "different js programmer needs to review your code" - if you don't know smth then you need to study it. That's a fundament of programming world(probably not only programming))

[arcatek]

Untrue. The ES5 standard contains most of the features required for any application (my main issue being the Date prototype which could easily be improved).

jQuery, Prototype and afaik Underscore helper functions have been wrote when the standard wasn't ready. Now that it is, developers should start using them.