I beg to differ with everyone above, the gauge may also be wrong.
On my 2.4 20v (thermostat already replaced), the needle sits just above 70, but the sensor reads a very healty 87-88 Celsius. If pushing the car, the needle goes from 70 to 90, which corresponds to an increase in the real temperature (from FiatEcuScan) of approximately five degrees, i.e. 92-93 C.
The lesson I learned, after spending nearly 100 EUR on a new thermostat - get a cable and a copy of FES and check the real readings before spending money on replacing parts.
My car's fuel consumption is not ideal (best I got was 6.7 l/100 km or 35 mpg - a 700 km motorway trip, most with cruise control at legal speeds), but I guess that's got more to do with my driving style...