Just got back from a Seattle to So Cal trip. I've been doing 99% city driving for the past year, so I've been getting terrible gas mileage; like in the 16 mpg range.
But during this trip I got an average of 31.5 mpg over the whole trip. My first tank I was at 245 at the halfway mark, and at 409 when the computer read 0 miles remaining; and drove it to 425 miles. When it was filled up (in Oregon so I couldn't pump it), only 12.377 gallons went in. If that were true, it'd be 34.3 mpg, but I definitely will not claim that. Just by knowing my car, I'd say he should've put in close to 13 gallons. My next tank was 389.9 miles on 13.5 gallons (28.9 mpg), which was probably a result of being underfilled at the first fill-up, and the last was 399.8 miles on 12.7 gallons (31.5 mpg). I just slightly topped off at the start, and slightly topped off at the end - so over the three tanks it should be a pretty accurate average. Needless to say I was very happy with the fuel efficiency.
For those wondering - I have an 07 MS3 now with ~5900 miles, MS-CAI, synthetic oil since 2500 miles, and the last reflash from the OBD-II compliance recall (have not had the fuel pump TSB re-flash). I generally did about 5 mph above the speed limit, except for the downhill areas where I let gravity take over. A/C was on for about 2/3 of the trip, since it was 113 degrees in So Cal. Did hit a fair bit of traffic on the 210 also; so that last tank at 31.5 mpg is pretty impressive. Oh, and my car was full because I was moving (but probably weighed less than having 3 adult passengers).