Hey Colin - thanks for reaching out.
Polymer has been growing exponentially, and is a major project here at Google. Here's a snapshot of the latest use of Polymer internally (y-axis unfortunately has to be removed, but purple is # of unique components, teal is # of projects, and projects is in the multiple 100's including some of the biggest by daily active users):

The Polymer team has doubled in size in the last year to over 20 engineers and is continuing to grow, and we'll certainly be having additional Summits (currently in the planning stages).
And I think most importantly, the biggest milestone of all is right around the corner as Eric mentions, with Custom Elements and Shadow DOM soon to be shipping broadly.
We completed a major planning phase in January and hashed out some top priorities for the first half of the year - we'll be posting this on Github and going over in more detail on a blog post very shortly.
Hope that helps a bit, and really glad to hear you've been enjoying using Polymer!
Taylor