I bought one of these at the beginning of the summer and I definitely noticed a fairly significant savings. In my case I updated from a really old, couldn't-be-programmed, thermostat right to one of these which almost certainly skews the results since any kind of programmable thermostat would have shown a savings.
I live in NJ and work in NYC so during the week I'm only home for a few hours, besides sleeping, and it learned my schedule on its own. When I get home it's just kicked in and started bringing the temperature down and it goes off shortly after I leave.
The only issue I had was during the first setup it mixed up the heater and air conditioning because of my settings. But I just restored and went back through and changed what I selected and all was well.
For anyone interested in this subject I'd highly recommend the Algorithm Design Manual by Steven Skiena[0]. He goes over this in pretty good detail in the first ~1/4 of the book. This was my first introduction to Algorithm Complexity Analysis and by the end of that section I already found myself looking at my code in a different light.
I live in NJ and work in NYC so during the week I'm only home for a few hours, besides sleeping, and it learned my schedule on its own. When I get home it's just kicked in and started bringing the temperature down and it goes off shortly after I leave.
The only issue I had was during the first setup it mixed up the heater and air conditioning because of my settings. But I just restored and went back through and changed what I selected and all was well.