Our Nissan is pretty accurate with the trip computer (I check it as always go full to full and have odometer - the odometer has also been checked by GPS and is correct to within 1%) - always within 1.5%. Some other vehicles I've driven aren't so great on the trip computer - one would almost think it's been tweaked for optimism! Something that doesn't help is when people "chip" their cars - because chipping fits between your ECU and airmass sensor it fools the ECU in to over-fueling, whilst miscalculating the total fuel added - so the trip computer mpg goes up, despite real mpg going down. (Remaps are the only decent tuning option).
Anyway, I digress. I don't have much time for GM, but the Cruze is a half-decent car with a decent engine. I wouldn't buy one, as GM's new line still hasn't exactly proven itself, but I can see why people would. Decent fuel economy, performance, quiet and mostly comfortable - could do a lot worse.