My old pre-ED 320d manual did about 44mpg over 35k miles. I had an ED 320d as a courtesy car once, it seemed to get closer to 50mpg on a run, driving it gently. Not a huge difference but I guess it would add up in time.
Current: Skoda Octavia Scout 4x4 DSG
Previous: F30 318d Sport, R56 MINI Dooper 2010, E93 325i M-Sport auto 2007, E91 320d SE 2005, E46 318Ci Coupe 2002