I think I achieved the record low mileage with very short commutes and pre-heating the cab when it was 30 degrees below zero here in Fargo in January and February, of 29 mpg. A few people, with good conditions, are coming in very close to those EPA figures. Consumer Reports said 44 mpg city/hwy average.
Basically, the first five minutes of driving, as the engine warms up in Phase I of its program, are likely to be 25 to 30 mpg. After that, the sky's the limit, depending on your driving conditions, ambient temperature, and driving style.
People are also reporting dramatic improvements in mileage after the car is well broken-in at a few thousand miles.
I have had my 2004 Prius for three weeks now and just filled up for the second time, my milage was 45.6mpg. Most of my driving is on the highway so I am happy with what I am getting. Sure beats the 14mpg my wife is getting with our Suburban, and the 17mpg I was getting with my Ford Windstar!
Here's some specs from our cars: displayed mpg (calculated mpg)
2003; 10149+ miles:
First fill-up: 48.8 (43.2)
Highest tank: 50.7 (47.4)
Highest round-trip: 52.7 over 103 miles
2004 w/17" wheels; 1119 miles:
First fill-up: 44.2 (38.8 )
Highest tank: 44.1 (43.0)
Current tank: 49.1 over 195.6 miles
This is all (mostly) without the A/C running. I noticed a big increase in mpg on the 2004 about 2 weeks ago when I increased the tire pressure to 42 front/40 rear; 2003 tire pressure is "above normal", but still below "safe max". We're planning on switching to synthetic oil as well on the next scheduled change.
Perhaps a few "sticky topics" for FAQ's like mpg would be useful?
Mid to high fifties driving conservatively in mixed driving conditions. 77 mph gets me in the mid forties but 65 mph gets me in the low fifties and 55 mph gets mid to high fifties. 45 mph with some stops nets me in the mid 60s.