Ok, yes for some reason I added the 2... just ignore that. I know it's looking for carbon monoxide.
Most people don't need the CO alarm, it's for people who regularly heat by burning stuff in their homes
As houses become more tightly sealed and more stuff becomes propane powered, it's important to have this warning. Most people have propane water heaters, many have propane stoves.
Also fire is kind of it's own alarm system, whereas CO is otherwise a lot more un-detectable, so it balances out in making just as much sense to warn about it when it's a cheap addition to sensors you already have.
And if you produce enough smoke to set off an alarm while cooking, you're doing something wrong
That's not necessarily the case. Some things may inherently put out more smoke than a vent may carry off - or in fact perhaps you ARE doing something wrong, in which case why have an alarm at all, because you obviously know the source of the smoke and just need to open a few windows.
They wouldn't already make smoke detectors with the ability to ignore smoke unless it were a useful feature, the Nest just makes it even more accessible and useful.
This thing really is a solution in search of a problem
That's where you are wrong. It doesn't NEED to search for problems, because common problems exist for countless people:
1) Which detector is triggering for (battery / smoke / whatever)?
2) How do I disable false alarms?
Those are real problems that lots of people have with the existing systems, quite frequently. And they are really annoying. Like all good problems the Nest iterates on current products to solve common problems people have with them.
I don't have a Nest thermostat myself because the kinds of issues it addresses, I don't feel like would apply well to me as I am not as habitual as most people and I also work at home a lot. But the smoke detectors are very tempting, to at least install in a few key locations (like the kitchen) and have something that's far less a pain in the ass to deal with and has really useful features (like the automatic motion nightlight).