fkeel:
what do you base your "what it should be" values on? I don't know the sensor you are using, but I would expect it to give higher readings when powered by 5v than when powered by 3.3vif you are powering it through the digital pin and connecting it to a common ground and have no other connections going on... there really is nothing which should be interfering with your readings...
The datasheet says it will output 10mV/ºC no matter what voltage it is fed, as long as it is within specs. I removed the resistor and the capacitor and the sensor reads between 22.80 and 24.26ºC. Not sure why there is such a difference.
Without the resistor and capacitor, I can use the +5V rail but not the GND rail. If I feed the rail with +3.3V, readings are off coming in at around 30ºC.
Boy, is this frustrating!!!