They have clearly paid a lot of attention to even the smallest details and if you like that kind of thing, a Nest Thermostat will make you very, very happy.
I even got a negative bill as my first month was billed on estimated usage. :-)
I live in NJ and work in NYC so during the week I'm only home for a few hours, besides sleeping, and it learned my schedule on its own. When I get home it's just kicked in and started bringing the temperature down and it goes off shortly after I leave.
The only issue I had was during the first setup it mixed up the heater and air conditioning because of my settings. But I just restored and went back through and changed what I selected and all was well.
When you're running the AC, it actually learns how long it can continue to cool by just running the fan due the the lingering coolness of the coils after the compressor has been running. This causes the AC compressor to run less while you're still able to be kept cool, at significant cost savings.
Your standard thermostats currently don't do this.
In my experience, yes. I left town for two weeks and forgot to turn on away mode. If I'd had a cheap one, I'd have paid for two weeks of A/C keeping my house at 72. Instead, I was able to remotely tell it to let the house get up to 85 before kicking in.
Auto-away does the same thing on a smaller scale on a near-daily basis for me, as well. We've got a pretty unsettled schedule, so it's a wonderful feature.
But on top of that it looks good in my high traffic hallway. Being in the hallway to my bathroom it acts as a nice night-light (it turns on when I step out of my bedroom to goto the bathroom and visa-versa) and overall has been a joy to work with.
You shouldn't, unless you can't run the wires to the same location for some reason.
From: http://www.nest.com/blog/2012/10/02/the-next-generation-nest...
I am pleased.
Radio Thermostat (http://www.radiothermostat.com/) makes a line that's not as pretty, but they provide a web/JSON interface that looks pretty interesting.
API doc: http://www.radiothermostat.com/documents/RTCOA%20WiFI%20API%...
here is a reference implementation https://gist.github.com/3808559
