While most of the country has been busy writing thank-you notes for holiday gifts, dedicated environmentalists have been writing letters to Grist. Many of those letters were precisely about the habit of exchanging costly presents, as readers responded in droves to Eric Brown's article on holiday consumption. Other readers weighed in on Cape Cod's battle over wind energy, on Arianna Huffington's anti-SUV campaign, and on why the Big Apple's subway system should be the pride of New Yorkers, among other topics. Check out our latest letter bag, only on the Grist Magazine website.