I own an Astra and I have to agree that 32/43 mpg (city/highway) is optimistic. That being said, my car currently has about 2100 kilometers on the odometer and I am seeing better gas mileage then I did when the car was spanking new. My first 2 tanks of gas didn't average much better then 9L/100KM. Recently I have seen an average of 8L/100 kilometers and that is combined city and highway. For pure highway driving, I now regularly see 35 mpg, and I have the auto tranny. I just need to keep it between 95-100 km/h. So far I really like this car, despite its tendancy to relax while taking off. But keep in mind it is made to be a high quality econo coupe and not a rocket like and SRT-4 or ION Redline/Cobalt SS.
So far, this car is worth my hard earned cash. If you are thinking of test driving one, go and do it for sure.