Even with new cars, model years are more important than ever. For instance, last year you might have seen a leftover 2011 Jeep Wrangler parked on the lot next to an identical-looking 2012 and thought, "What's the difference?" Oh, about 83 horsepower and an extra gear in the automatic transmission. A similar situation faced Mustang buyers last year: From one model year to the next, the engines changed so dramatically that the base V-6 was actually quicker than the prior year's V-8-powered GT. Conversely, sometimes you can score a deal on a leftover that's functionally identical to the latest model. You just have to know what you're looking at.