I've been to classes before that really changed my shooting. I'd say that the first Aim Fast, Hit Fast class with ToddG and last year's Advanced Tactical Pistol Skills class with Ernest Langdon were pivotal moments in my skill with shooting a handgun.
ECQC changed my life.
For instance, since ECQC I've finally started practicing something I'd long preached and began carrying a can of Fox Labs OC around with me. It's become more important to me to have a solid middle ground option between "harsh language" and "bust a cap in someone's ass".
It's made me think a lot more about deescalation, how persistence does not automatically equal threat, that presenting a weapon (or even revealing its presence) without the space or time to employ it correctly can cause a lot more problems than it solves. Letting a guy who's within a dozen feet of you know you have a gun doesn't necessarily deter him; it just lets him know you have a gun. It's up to him whether that's a deterrent or not.
Physical fitness has become more important to me, too. All tangled up under someone who's beating your ass and about to pull your gun out and shoot you with it isn't the time to find out you're completely out of breath, too.
Lots and lots more in this vein, but I just wanted to dash some thoughts off this morning.