we are close to 4500 miles now and our average is about 27.1 MPG. On a long trip I was able to consistently get 31-32 MPG at 75 MPG in both directions, so I'm sure I could have gotton the advertised 34 MPG on the freeway if I kept the speed down below 70. Was doing exactly 75 MPH according to my GPS which indicates that my speedometer was showing 3-4 MPH faster (~79 MPH).
In the city, I think for my driving style 23 MPG is readily acheiveable if I'm conscious of saving fuel. I can get 24 if I try very hard. I usually get 22 in the city because I like to have a little fun.
So overall, driven semi agressively, I'm about 2 MPG less than EPA estimates. Can't complain, but usually I can easily acheive EPA estimates with the same driving style. Keep in mind that I have an S-drive. Must be the turbo! (read below)
I think the numbers people are reporting are very different mostly because of driving style. I can easily get lower numbers if I drive more aggressively. This seems to be especially the case with turbo engines that have the potential to be efficient if driven conservatively and quite the contrary if driven aggressively. I take smaller hit from driving NA cars (M54 BMW) agressively. With turbo cars, you just have to keep in mind thay the reduction in gas mileage is greater than a NA car when driven aggressively.