Just got an email subject Here's $70 off the latest Nest Learning Thermostat. The link contains a unique coupon code for $70 off Nest Gen 3 which seems to be a good deal. Looks like free shipping.
Expires September 1. Promotion valid only for a single purchase of an eligible item on nest.com. Offer is as stated, and is not redeemable for cash, reloadable or refundable. Cannot be resold, exchanged or transferred for value, except as required by law. Nest may amend or suspend this offer without liability to any customer or potential customer.
Link for reference.