That's one of those "fail-safe" thermostats. It is stuck open but that brass colored clip is whats holding it open. Those are purposely made to hold the thermostat open in the event of a failure/overheat. Now that I think about it I have never removed one of those that was not in the fail-safe failure position, they seem to "fail" a lot. I would get a regular OEM stat to replace it.
With a good operating thermostat you should notice better fuel economy since the engine will run at operating temps. You should also have a better working and hotter heater.