The sky is the limit, node-webkit is indeed very powerful when you know what you're doing.

For the build process: just try it with brunch, e.g.: with my skeleton (a simple todo app is included for playing around). It will take ~4sec to start up initially, but then work close to perceived realtime, taking 50ms or so on my machine to reflect any changes you do, plus: livereload automatically the browser window, so you actually save the "press reload" step in most cases.

And: since i'm using only meta-languages that require a compile-step (!), i have basically a useful error-checking (incl. linting!) on coding time, without time-intensive inspecting the result in-browser. Do not underestimate this. Sure, finally i have to confirm in the browser (and/or testsuite) that everything works, but typos and other common bugs are "growled" as i type.