We just bought our used 2007 Impala LT w/ the 3.9L (Active Fuel Management system)engine at the end of September 2009. So far we've put on 4K in 2 1/2 months of mixed driving and averaged 23 MPG (which is not bad for such a large car). The Bose sound system is great, as are the large controls and placement of the controls. My only gripe would be the soft touring suspension (I was used to driving a VW Jetta before) and the seats could be more supportive (could also use Memory seating). Otherwise, this a great car for the money and features.
Bose Sound System, Remote Start, Gauge display, and Control/Knob layout.
More supportive front seats, automatic climate control, tighter suspension/springs, and more feedback from the steering.