Been using Polymer for the last year and loving it. Happy to do very little to get my element portfolio progressively over to litElement. Congrats to the polymer project team on getting this out there!
Hi, I've been developing in Polymer / Web Components since early February. I can say that it seems like polymer prior to version 1 was the wild west and changing all the time. Polymer 2 is very close to being released (rc7 I believe) and while I'm only developing in Polymer 1, 2 isn't very different. If anything, they've only removed things.
earth.google.com launched last week and is amazing / built out of web components. I'm still getting used to doing full one-page apps in it but after being about 30 elements into development I can say I can't go back to the world prior to this approach. Starting with the smallest atom-esk elements and then building up makes building new things faster and faster then the previous build. We're using it to build an open source edtech platform, polymer is allowing us to open source our designed elements individually so that they can also be built on top of / remixed.
webcomponents.org also is over 800 elements now and I've found some really good ones starting to show up from the general population outside of just google's core polymer team which is really promising.