The offer is good as long as you don't drive more than 4,000 miles and there is less than $300 worth of damage to the vehicle. You must also keep the vehicle for at least 30 days before returning it.
The refund includes the full purchase price plus any sales tax, however, it doesn't include any other dealer fees, title, registration, and other taxes. That means you may still end up paying several hundred dollars out of pocket if you do return the vehicle. The offer is good through September 4, 2012.
In addition, GM is also offering discounted no-haggle prices on all 2012 Chevrolet models. The no-haggle prices aren't that great in my opinion, but keep in mind that you can still negotiate below these prices.
I recommend you use the CarWoo Deal Finder to get the best prices on these vehicles.