After ComEd's electricity rebate of $100, and Northshore Gas' $20 rebate... the $200 2nd Gen Nest totals only $80. So it was an easy choice.
For the first 3 weeks, the Nest was playing around with the furnace. By this, I mean that it would turn it on as needed but shut down after a few minutes. Then start up again. This made me initially think that the furnace or Nest was broken. But as the days went by, it learned how our furnace worked and how long it took to heat the house, and when to start heating up.
Granted it has been a mild winter this year, there have only been a couple of times when I've had to adjust the heat up and only for a few minutes.
The Auto Away feature is quite useful. You never have to worry about leaving your heat on, and even if you do, a quick check on the app allows you to switch off your heat in case it hadn't detected you weren't home. It gets it right about 85% of the time so far.
Savings? YMMV. If you keep your heat at 85ºF (30ºC) in the winter all the time, then you probably won't notice much savings. So far, we've been quite happy with a 68ºF (20ºC) setting for early am and early pm settings and 65ºF(18ºC) for most of the day. The weekly report shows our furnace on for about 2-3 hours a day total. Probably savings of a few minutes every day. It may not seem like much but the remote feature and learning function are worth it.
All in all, it's worth it. If $250 is too much for the current model, get the 2nd gen model. The smaller screen isn't that inconvenient and is $50 cheaper. Rebates bring the total cost of ownership under $100. It looks good, works well, and is the easiest connected thermostat to learn.