Saw this in a coworker's brand new Subaru Legacy
The left graph is average MPG, center is instant MPG, and the right is % acceleration. He's not a gentle driver and made quite a bit of use of the turbo (even when only going 20' to slam on the brakes and turn), but still manages to average ~20 MPG. It was also fun watching the instant go from 40+ to 0 to 10 to 30 which was just about the complete opposite of the acceleration meter.
He might not be using it, but I figure if it's there someone might be using it to think "gee, I get better milage driving this way..."
