I just checked my 2004 Road King Custom about 3 weeks ago. It came in at 47 MPG and some change. All stock other then the V&H pipes and the screaming eagle air filter. Not to shabby as far as I am concerned.
A riding bud gets 48 to 50 regularly on his Softail Custom with windshield and saddle bags. I got 45 to 48 regularly on my '07 Heritage. I just did 800 miles on the new '09 Ultra and got routinely mid-40s (42 to 46) with a high of 48.5 on one stretch (60 to 65 mph with a slight -- 5 mph -- tailwind). Mileage drops pretty quickly when speeds hit 70 or more. Worst I got was 39 on a stretch coming up hill from St George to Cedar City, UT, when I climbed from around 2000 feet to over 6000 feet and had a headwind.