I'm a Mac developer and I have to tell you that writing Cocoa apps in JavaScript is not great because JavaScript is not a great language. I would much prefer Ruby, Python or C# syntax than JavaScript syntax.
It's also a reason why JSCoca hasn't taken off despite being available for almost 2 years now and why MacRuby is such a promising, although not yet production quality, project.
Nitpicking: Palm didn't bet on JS but on HTML stack (of which JS is a part, but not the whole).
Unfortunately, your opinion isn't very popular around here. People here don't seem to want to accept the fact that javascript was never designed to be a scalable general purpose language for writing large applications. It has slowly evolved over time, but is still not there.
I hope something like Google'ss NaCL becomes popular, and instead of javascript slowly creeping to the server/desktop/phone because we have no choice in browser-land, the browser opens itself up to all computer languages so javascript can start feeling some competition. I even think this would be good for javascript, as it would spur the language to evolve faster.
Palm is already betting on JS, google too, so it is just a matter of time when the mobile world uses a flavor of JS for apps.