Interesting...I was going to delay post until I had some "actual" numbers...but since it popped up:
On June 9 (see earlier post in this thread) I attempted to duplicate the same set of circumstances observed by Yves. So far the MPG for this tank (which is about 3/4 gone) is ~58.9 in mixed driving. Which is pretty much equivalent to the last tank.
I also had a chance to take the car on my 50 mile round trip commute to work. I achieved 75.3 MPG on the loop. My personal best so far is 76.0MPG. There was light rain and wet road conditions for the first half of the 75.3 MPG loop while the conditions on my "best" were excellent for the entire loop.
So far, I have not seen anything that I would consider "significant" in the form of mileage gains. However, as I have pointed out and say again...my test was far from scientific. Also I was getting nearly the mileage normally which Yves claimed his car jumped to.
Lastly, Yves...About the regen braking. What I found with my car was when driving down the road, throttle slightly open, and lightly stepped on the brake (RPM ~2500) no regen braking. As soon as I would lift on the throttle (ie ECU would see 0% open) the regen braking would kick in until the engine RPM fell below the cutoff point.
If you are seeing regen with the throttle partly open, is it possible your TPS is mis-adjusted or the ECU is not getting the correct voltage (ie faulty wire?) Generally TPS voltage is ~.5V closed and 4.5V at WOT. IF you had a high resistance connection, bad ground, etc... that voltage may be reduced and the ECU would think the throttle closed earlier. It could be a situation where a component is faulty and giving you poor mileage, while the "fix" is just getting everything back to normal for a while.
I will admit that I am not a big "featherfoot" but my car still manages 55-57 MPG on the interstate (70-75MPH), 70-75MPG on the secondary highways (60-65MPH), and about 60MPG around town.
I will give "The Yves Method" more testing with the next tank of gas. Keep us posted on any additional discoveries!