The file is at the printer!
It seems these things always take longer than you expect, but the printer now has the book file and is making a proof copy. Once that's signed off, the full print run can begin. We're in the last stages!
Unlike last time, when the book was printed in China, this time we're using a US-based printer, so the shipping time from the printer to Make That Thing for distribution to backers should be a lot quicker. I'll keep you up to date!