Depends on how accurate the thermistor itself is - components like that are usually made to a 5% tolerance. That's 5% of the overall resistance value though, which could be thousands of ohms; I don't know how that might translate to a temperature though.
It also depends on how close the thermistor is to the processor, and what the processor substrate is made of (ceramic or organic.)
BTW - anyone know why it's called "organic"?