I'll ring in at 44-46MPG with 91 Octane and PCIII with Stock map and Stock '05FJR on Pilot Roads. Not bad I think. I wish that some of the above posts would say Octane, PCIII or not, and Cans or not, and Tires too. In my opinion these all make a difference.
Octane makes no difference whatsoever. Nor will cans, as they are not the restriction - the catalytic converter is. I don't see how different brands of tires will change anything either, assuming you stay in the sport-touring category. Tire pressure could definitely make a difference, however, albeit a very small one.
My 04 in stock form got in the high 40s. When I farkled with th PCIII and Holeshots, fuel mile went down approximately 15% to the low 40s.
From my experience, the average high speed someone runs at can make a significant difference in fuel mileage. Say 65 vs 85. Around here, I have also notices seasonal changes. Whether that's because the seasonal changes in the blend of gas or colder weather/running, I don't know.
I'll say it now, as I have said it a million times before - ELEVATION, or more properly density altitude makes a HUGE difference in fuel mileage. The less air, the less resistance. I have always obtained my high mileage tanks (high 40s to low 50s) at higher eleveations.