I control my Nest on my Apple Watch using the IFTTT Do Button app (iTunes link), which is compatible with the watch.
I have two buttons ("recipies") in the watch app- one to set the temp to 15 degrees and the other to set it to 21.5, which basically reflect my flat's 'on' and 'off' temperatures.
It is really cool tapping the button on my wrist and seeing the Nest light up and do its thing.
I asked nest about this and got this repsonse:
With the tone of that it seems that Apple and Nest relationship is going no where.
Apple: "Nest use Homekit"
Nest: "Apple, join 'works with Nest'"
Might sell the nest and get the Honeywell now.
If you just come and go from your house at the same time all the time, then I can see that. Or if you live in a temperate climate where you don't experience extremes in the house if you're away.
But if you travel on a non-regular schedule it is nice to tell the house you're not away anymore when you're coming from the airport so it's not freezing or boiling.