I just wanted to share my experience from this past weekend...
As I mentioned before, I had quite a bit of work done on my boots weekend before last, but I didn't have a chance to ski them until this weekend. Got out on the slopes, which despite being greens were really pretty cruddy and choppy and lumpy by the time I got done wrangling kids to where they needed to be, and I just couldn't seem to get comfy on my skis. It didn't feel like my boots were wrong, exactly, but it felt like my feet were sort of...twisting in a way they shouldn't and I didn't feel like I was staying centered on my skis. I went to another lift with runs that were less cruddy, noticed it was getting a bit better but I still wasn't quite convinced that everything was hunky dory. I suddenly realized I was out of time and going to be late to pick up a kid from a lesson, so I hopped off at the lift midpoint and started skiing down (a blue run) as fast as I could, without thinking about feet or boots or skis, and then all of a sudden OOOOHHHHH, everything came together and my feet relaxed and everything felt SO perfect and in control even though I was skiing faster and steeper than I had all day.
In retrospect, I think I was so used to being on my inside edges due to my overpronation, that I was pressing down on the inside of my skis to get the same balance point on my skis, and then trying to ski by lifting my big toes way too much while still pressing down on the inside of my skis with the balls of my feet. I had trained myself to compensate for standing wrong on my skis, so now I have to train myself out of my bad foot habits (which an instructor warned me this year that I'd have to do after getting my boots fitted, but he also indicated that I likely wouldn't improve until I did because the overpronation was keeping me from easily keeping my skis flat to scrub speed - when things got going fast I'd catch an inside edge). It seems to me that a properly fitted boot means not having to focus on keeping my foot in the right place in the boot or twisting my foot in crazy positions to get everything into place.