I got 27.9 from my last fillup on my wrx. That's from 319 miles of mixed city/hwy Los Angeles driving. I've averaged a little over 24 mpg in the last 1800 miles since I purchased the car. I noticed that it's a little less fuel efficient in the mornings when it's cooler.
I am getting 21.3 by the little computer thing overall. I get about 19+ normwl city driving and 24+ on the highway @ 75+mph. I know in the past, staying at 75 or below would increase you milage to around 28mpg's. This is with the VDC on. I have heard that you get better milage if the VDC is off so I am trying to turn it off all the time to see if it makes a difference. I am going to go on a 1700 road trip soon. I am going to turn off the VDC for at least on full Highway section to see if the is really any difference.