So far I've only used it for a tiny project.
The documentation is good. Routing is not straightforward since it's BYO. I did manage to get something working though. I haven't had to ask the community anything.
I wrote an article about my experience with Polymer but this was an experiment and probably doesn't follow best practices.
I would use Polymer again if I had an appropriate project. I also plan to try a similar framework named Riot.js. Riot seems to be simpler with fewer drawbacks.