I've used Polymer in two projects now. It's simply not ready for real production use in my opinion. Too many issues overriding / styling their components (modal is awkward as hell to style the content) and it's simply too slow on start-up. Firefox literally freezes for many seconds to load several components (chrome doesn't but it's still not very fast).

I want web components to be a thing but Polymer is not the path forward in its current state.