I installed one of these beauties over the weekend. It was easy to install, and has a beautiful user interface that blows every other programmable thermostat away. And I can change it via a web interface, which is handy if I forgot to change it before I left town.
It remains to be seen if it actually saves money. It is a very satisfying piece of gear, though. It has that Apple kind of industrial design, which is unsurprising since it was designed by ex-Apple folks. It is currently in its learning mode where it learns where we like to set it at different times and days of the week. Maybe these guys can turn their attention to lawn sprinkler controls next, as that is another industrial design / user interface nightmare.