Just to be clear, this is the ECT, not the temperature sender:

I replaced my ECT today and it's a b**ch to get to. It is located about halfway down on the driver side of the engine, facing the firewall. From what I understand what it does is sense the coolant temperature, and the computer adjusts the spark & fuel and such based on that (and many other) reading.
I've been having higher than normal temp readings and it's been taking longer to start than it used to, so I'm hoping replacing the ECT will help.