I think writing one language both server and client is a big yes for node.js, but looking at my client-side code vs my server code (and I'm writing Javascript since 2001, way before I learned Java) I come to the understanding why Google are investing so much in Dart / GWT (which I think are not there yet)

If Scala/Haskell/Go would become more mainstream, and had a very straight forward / magic-free 1:1 conversion to javascript, then node.js will have much less appeal to me.