That's true, I shouldn't mix up the two - the real complaint is about the tooling, but it's in refactoring tasks that I really feel it. For example, say I want to rename a class: If I'm in java/eclipse I can command-option-R, type the name, and press enter. Total time about 2 seconds. If I'm in sproutcore I have to search/replace the whole project searching for references which takes minutes and is tedious.

The reason it is difficult is because you can't use any of js tools that leverage a js interpreter - your code isn't valid until it's run through the sproutcore build system (which, as previously mentioned, is pretty slow).