sender and sensor
I think that MadDog is right in that it's nothing to lose sleep over.
My guage uased to read straight up, then began a downward drift until one day it always read cool. So I replaced the temp sender (the one-terminal input; $11.50) and now I have much more confidence that the guage is accurate: it goes to about "M" at idle on hot days (I have u-pulleys, so the water pump isn't going as fast), but then coasts back down once I reach "usual" operating temperature.
Seeing that the sender was getting a false reading, I also replaced the sensor (the two-terminal device; $30) since this is the unit that delivers input to the EEC. I figured if one thing was crapping out, maybe the other one was as well.