I've been using Polymer for a few months now after following the WebComponent spec for quite a while, and I'm really liking what I'm seeing.

While it can admittedly lend itself to a very Java Swing-feeling development flow, that's a breath of fresh air compared to the traditional mess of web code I usually end up with.

WebComponents in general (and Polymer as a particular library on top of them) I feel are going to be a 10x force multiplier for web development.