I never understood this. Why would I care what the temp is when im not there?
Couple of reasons: to make sure I'm not paying to heat/cool the house if no one is there and in the winter I would check the house temp before I left work and decide if I wanted to turn the thermostat on to warm up the house for my return.
The Nest is a really cool device plus they send you a monthly email. on your energy usage.