On my first drive (home from the dealership) with my 170TDI Scirocco on a 16 mile journey I got 53mpg! I admit is was a little more serene than most journeys. I found that the economy hasn't improved much with bedding in but the performance has. I found that on the 170, the engine seemed like it had been artificially retarded during the first 500 miles, it seemed really tight compared to the previous one (140TDI Scirocco), I was really disappointed, it seemed no more powerful than the 140. 500 miles passed and then almost as if a switch had been flicked at 500 miles it was like a whole different engine. Maybe the car was performing a "running in" program before it lets you put your foot down? Seems ridiculous I know, but the difference was not gradual, it was pretty much instantaneous.
Poor fuel economy has been discuss frequently on the VWAudi forum and a few other places. "Honest John" website is logging true mpg vs claimed and most 150PS GT owners are seeing less than 50mpg right now. In my experience I have seen a 5% difference between summer and winter mpgs on TDIs.