I'm disappointed by the acquisition, as I just installed a Nest a little over a month ago. Had Google purchased them prior, I would not have gotten it.
I fully expect Google to plunder Nest for useful tech and engineers, holding on to the company for four or five years. They'll get what they need out of it, and then probably spin it back out on its own or sell it to another investor, but either way, it'll be a shadow of what it could've been.
Sketchup went the same way. Awesome, simple software, held on for a few years, then spun back out, and it's never been quite the same. Its mission is different now.
Or maybe they'll just shut it down when it's not a shiny new toy any more, as with Reader and Wave and countless other tools.
Google isn't a great innovator any more. They're a holding company, and a venture capital company. They have a reputation for making innovative products...and then killing them, with no replacement. I don't trust them, and my concerns have nothing to do with privacy, but everything to do with the way they treat consumers.