I haven't built an application in Polymer yet (though I did have a good experience building a small application about a year and a half ago with Dart's WebUI library, which implemented a lot of the Web Component features before Polymer and the web browser layer was ready), so I don't have any advice on how ready Polymer is for prime-time yet.
What I will say is that we should remember that Web Components is where the web platform is going. This isn't some one-off library by Google; both Chrome and Firefox are getting all of the web component primitives built into the browser, and it looks promising that we'll see them arrive in IE and Safari as well. Polymer is some sugar on top of those primitives to make them easier to work with, but in any case, the next generation of web apps will start using web components and probably some library like Polymer or XTags. The time to start learning and playing around with web components is now, even if it's not time to build massive applications in them quite yet.
What I will say is that we should remember that Web Components is where the web platform is going. This isn't some one-off library by Google; both Chrome and Firefox are getting all of the web component primitives built into the browser, and it looks promising that we'll see them arrive in IE and Safari as well. Polymer is some sugar on top of those primitives to make them easier to work with, but in any case, the next generation of web apps will start using web components and probably some library like Polymer or XTags. The time to start learning and playing around with web components is now, even if it's not time to build massive applications in them quite yet.