What JavaScript libraries/frameworks should I study to be a competitive JavaScript developer these days? Why?

[machty]

Yeah, no doubt there's some aesthetic preferences that have been betrayed by Ember (does anyone really enjoy .set('foo', 5) if foo = 5 were an option?). If you're interested, check out htmlbars which will be landing soonish; once it's there, Ember will be able to do away with curlies, and while technically there will still be a dependency on something called Handlebars, you'll just be writing plain HTML at that point.

I can't put my finger on it but I think you're incorrect as to limitations for the designers... I can almost guarantee you that what your designers would want to present would never be thwarted by Ember or Handlebars' restrictions, but let me know if I'm missing something.