Welcome tvent. I'm glad you're here -- actually it's perfectly timed. I review rental cars in this tread:
http://www.gassavers.org/forum_topic..._analysis.html and had some inconclusive MPG results on the Aveo. Keep us posted on your progress. The "Gaslog" is a great way to track your progress. Let us know what you think about it so far, odometer reading, etc.
kickflipjr: I think you'll enjoy the ride. My half-brother bought the 5-door new as his Dad has worked for GM for 35+ years and got mega-discounts. He drives quite a few miles per day commuting and claims good mileage (I don't have a number). If you do Interstate driving, you'll have to work at keeping it in the lane with the soft suspension and crosswinds. Otherwise, I'd drive one for a company car if I had to (and really wouldn't complain about it). The old Cavalier was horrid -- my old neighbor had one as a company car. I'd kill myself.
edit: tvent - if you're serious about improving your economy, the ScanGauge is the best investment you could buy. I would hang around a while, see if you continue with the fuel economy interest, and look for a good deal on one. It changed my FE by at least +5 so I can adapt my driving style. Good luck!