I've found that I get pretty close to the 47/48 MPG . . . IF (and this is a big IF):

• I stop driving like a maniac (80 MPH is more my speed)
• I drive somewhere flat (my neighborhood is hilly)
• I don't use the air conditioning.

I've gotten as high as 69 MPG in the utmost perfect conditions (I did a 5 hour drive, no stops, with the cruise control pegged at 57 MPH, in warm/dry weather and no AC).

I usually get between 40-44 MPG because I speed (when it's an option), live in a hilly area, and encounter a lot of stop-and-go traffic.