mine is now installed - here are some first impressions*
installation
Ordered on the 10th installed on the 28th
it looked pretty straightforward, although it was done by an installer: in my case simply replace the existing Honneywell wifi receiver with the Nest Link device. It was done in under 15 mins, allowing for a couple of trips up and down to the attic.
The actual process after ordering was pretty smooth - 5 mins after I put my order online I got a pre-emptive auto apology saying they were a bit behind with the installs but would be in touch as soon as they could. Not entirely surprising just after launching the product.
I gave it a few days and emailed asking how close they were to allocating install slots and as a result I was told someone would be in touch the following day. It seems my email crossed with the normal scheduling because the next day I got two appointments from different firms.
I declined one, and selected three dates/install time options. I was emailed a day later when my preferred date was confirmed. They promised to call half an hour before they arrived, which they did. The installer was polite and helpful and was quite obviously prepared to spend 20 mins explain how it all worked, but once we'd established I was happy to figure it out on my own was done in 2.
So overall, I would give the service 8/10 (2 knocked off for the slight delay). The only mild annoyance is that I have subsequently had a flurry of unnecessary calls and emails from nest apologizing for the "mess" that they made of the installs, when from my perspective it had all gone rather well. I suppose some people were more annoyed than i was.
hardware
seems to be well made, and is satisfying to use - the front of the device is like a big button and the aluminium trim is a big dial.
The tear-down report here concludes it was thoughtfully put together:
http://www.ifixit.com/Teardown/Nest+Learning+Thermostat+2nd+Generation+Teardown/13818
locating the thermostat controller
the controller works on 12v and there are three options:
1. if you have a wired controller today it can be replaced in its current location (the wifi receiver will also be installed between the boiler and the controller and it will transform the current to 12v. Apparently the nest will still communicate over wifi despite being attached by wires)
2. buy a stand and plug it into a socket
3. Screw it to the wall and then plug it in with the flex trailing down the wall.
option 3 would look ridiculous in most situations, so it is hard to believe many people will do it, in which case people replacing a wireless thermostats are pretty much required to buy the (eye wateringly expensive) stand
it is a pity, therefore, that this is not made clearer in the ordering processes. Particularly for numpties like me who - despite knowing they will need a stand - don't remember until 5 seconds after submitting the order and therefore have to do a second order for the stand and pay an unnecessary delivery charge. grrr
web software
underwhelming, and the software geniuses that designed the scheduler have managed to make it far worse than the experience on my old white plastic honneywell thermostat controller (nice and simple: +/- for the time, option to copy one day from the other).
The nest experience is click,click, drag, drag again (the blob to show you what time you have selected expands to cover the scale so you can't see what you are doing), click click, drag, accept, click etc etc.
Why set the a schedule when the whole point is that it is supposed to do it automagically? Because there is a period when the creepy thing has not spied enough on you and yours to know what you want and there is thus nothing to stop it firing up your noisy central heating system in the middle of the night.
Will I ever tire of being able to set the temperature in my house on the web? Yes.
worth the £179?
probably not. If, as mentioned above, you already have a programmable thermostat it is unlikely to pay for itself any time soon. Allowing for the fact the undiscounted price with install is now £249 with another 30 quid for the stand and the financial case is looking pretty shaky.
Although, having said that, my neighbour round the back whose spare keys we have in case of emergencies did ring up the other day on the way back from a week away visiting relatives, and - having enquired about the weather - asked if my missus wouldn't mind popping round and turning on the heating so they didn't arrive to a cold house. Bloody cheek, but at least a real world justification for the invention of an internet enabled thermostat.
Finally, it does look cool. And who knows with a few more wifi receivers the boffins might extend the device to control other things also?
(* note UK install)