It's becoming clear to me that many people are commenting on this product but few actually own one. I got my two Nests on the third week of January so I've had a 3+ months of usage out of them. My overall impression: outstanding.
A little background...three years ago I went to Home Depot looking for a better, more energy efficient household thermostat after talking to my wife who was in the middle of her Ph.D. program in environmental management. I ended up buying what was state of the art then...two of Honeywell's wall units. The first problem with them is that Honeywell expects experienced HVAC people to install them. So there's no effort to demystify the process for DIYers. I ended up calling my HVAC guy and having him put them in. But that was just the start. Now I must say, the Honeywells always worked as advertised. The problem is that the user interface is such crap that even after having the instruction booklet next to my bed for some reading for a week, I never wanted to really engage the thing. And worse, it was so complex I knew my wife wouldn't want to fool with it either. So while you could program it for weekdays and weekends, what you really find yourself doing was just sticking this thing on "hold", meaning it would hold whatever temperature you selected at that time. For the $300 I spent on the two units not to mention the install fee, I was literally no better than the older units I replaced them with.
When the Nests finally came in January, I installed the first one in the evening using the online instructions. The whole operation worked great as it recognized the wires and set up the unit, asking me whether I wanted Farenheit or Celcius, the particulars of the WiFi network and the zip code. I mated it to the Nest account I had previously created. After about 20 minutes of it downloading firmware updates and flashing itself, it settled into the initial learning mode. During the install of the second Nest, I ran into trouble. The upstairs wiring diagram had something the downstairs didn't have, a fifth wire for Common. That confused the Nest since it knew it was connected to Common but there was no power on the circuit. A quick call to tech support isolated the cause...Common wasn't connected to anything at the HVAC unit! This apparently happened a lot with customers but it was nice for support to know this. Disconnecting the wire fixed the issue and the second Nest was up and running.
I would classify the Nest as an evolving product, in a good way. There have been a number of firmware upgrades since purchase. I began with the 1.0 code base in which the Nest updated immediately to 1.04 upon install. A week later the 1.1 code base shipped which turned into the only snafu I've had with the product. The Nest units were supposed to find a certain server at Nest HQ to communicate to...a server that had been decommissioned. That led the units in customer hands try and try and try to establish connections until the battery in the units fell below a certain level. When that happens, the Nests drop off Wifi to save battery life and in many cases, just shut down all together to preserve power. The problem was quickly solved on Nest's data center's end (and fixed with another firmware patch on the Nests in the field), but for customers with dead Nests or non-working Wifi, the solution was to unhook the unit off the wall from the base and hook the Nest up to a USB port with 5V of power. After about 30-60 minutes, the unit was back in action. It was an unfortunate lesson for Nest but it was a good thing they put USB ports on the back of the units in case you needed to recharge them (normally Nests charge themselves by trickle charging against the current provided on the HVAC's control wires.
Since then there have been no problems. Even better, we've seen energy savings of about 20% in the winter heating months (about $40-$45) a month in my house. I'm still trying to assess savings data from AC usage. My electric power company's monthly usage data in relation to average temperature data is a little hard to understand versus our gas company that made the comparison a lot easier. As for day to day use, control of the household environment is easy through the interface on the Nest dial or through the iPhone/iPad interface. When the 2.0 code base dropped, we got the ability to see exactly how many hours a day (and when) your HVAC units are really running (versus just spinning the fans). Previously you only got an approximate idea that you were saving energy through temperature choices and feedback (although it did tell you how many hours the HVAC unit ran). Now it shows when temp changes happened according to the schedule and how that affected it turning the HVAC on or off. This is extremely powerful. The latest feature that we got in the 2.1 code base was Airwave, which basically is the Nest knowing that during the summer, if it turns off the AC compressor, that compressor is still cold for several minutes, meaning you can still blow cold air past it and cool the house. Pretty slick.
The latest feature is new in the last two weeks and something I've wanted every since the Nest arrived: monthly analytics. You get a summary of how long the HVAC ran for in hours (separate readings for heating and cooling). You also get gamification data like how many "leafs" you earned for being energy efficient as opposed to other Nest owners. Lastly, you learn how often and how long auto-away kicked in, or if you manually set the Away function if you stepped away for longer periods of time. And yes, if you set one unit for "Away", the entire house shuts down without you having to visit every nest you own...as it should work.
Our Nests are teaching us how our house uses energy, what temperature changes mean to our usage profile, and is easy enough for the entire family to use. And yes, we're saving money too and somehow they made it fun. Highly recommended.