I have Nest, and as a thermostat it is definitely one of the best looking and working ones out there as of yet, but Nest oversells itself as a "savior" of the environment and your money.
First, it is not really intelligent. Yes it does set up a schedule as you manually adjust it for the first few weeks, but then it NEVER changes your schedule, even if you do. Once the "learning" period is over, the schedule will be unchanged even after several weeks of manually adjusting it when I started working at a new job and I left and arrived at different times. Yes I can manually adjust it or put it back into learning mode, but that is not the point of a supposedly "smart" thermostat.
Also Nest once boasted of a feature to recognize and adjust to local weather conditions, this is false. Nest is no more aware of the local weather then you are, and too often I see people running their AC or heat when the temperature outside is actually cooler or hotter then the temperature they set it at. A "Smart" thermostat should just tell you to open your windows once in a while.
The "leafs" feature of Nest is dumb because there are several months a year where I don't need to heat or cool the home, I can just open the windows, but during these months when I have the Nest thermostat off, it doesn't report my usage as being "eco-friendly", even though I am using NO energy. Also during these months my Nest will run out of power because modern HVAC systems don't have a dedicated powered wired to the thermostat.
The remote capabilities of the nest are cool, but I have only used this feature a few times in the 2 years I have owned it. Coming home from a tropical vacation was nice to have the house toasty warm in the middle of winter as the plane parked at the arrival terminal, but rarely have I ever needed to adjust the temp remotely, or even look at the Nest status outside of being at home.
I am not saying that Apple will do something mediocre, but coming out with a "Smart" thermostat for the sake of competing with Nest is certainly not in Apple's best interests. However coming out with a thermostat which can actually save you money and the environment by knowing how to adjust itself based on current weather and ALWAYS observing your schedule and presence is the only way I would replace my Nest with something from Apple.