Why Stack and Tilt?
I saw my swing on video late 2008 and didn't like what I saw. Even though I'm a low single figure player I realised that what I had wasn't going to get much better... at least not any more consistent. I had 1000's of swing thoughts, little changes here and there and always seemed to be working on something new or different, I'd have one little thought that got me through each round and even that seemed to change every round.
But there was one thing that I just couldn't figure out... the backswing. I simply couldn't get my head to do the geometry of it. How is it possible to tip your right shoulder lower than your left, lean your spine 5-10° away from the target, bend forward at the hips and then rotate around your spine whilst moving your weight to the right side... chest over your right hip. Even if I made it there I couldn't figure out how I was supposed to uncoil, get the club square, get AHEAD of the ball before hitting it without sliding, and end up balanced on my extremely twisted left foot. It made no sense. Sure I could hit the ball - I just couldn't figure out how!
Every now and then I'd hit a fat shot, or a thin one.... sometimes I'd lose my rythm completely and hardly be able to hit the ball without scuffing the ground a few inches behind the ball. Handicaps don't stretch that far when you've only got a couple of shots to play with.
So I started looking into it somewhat, spine angle, posture, weight shift etc and found stack and tilt, it really made sense.
The thing that got me completely sold (and I'm going to share that with you) is the turn into the backswing. We've all seen people warming up at the range with a club across their chest, turning back and forth, pretending that they know what they're doing before they step up and slice one over the fence.
Well let's take a look at that drill and see if it has any use... (you can do this infront of your PC with an imaginary club and ball if you like)
Here's the picture so you know what we're talking about..

OK, kick back that chair you're sitting on and let's pretend...
Stand up straight with your arms across your chest, imagine you have the club across your chest and there is a ball in front of you right in the middle of your stance, right under your nose. Bend forward a little at the waist and flex your knees into your address position... You're going to hit a good shot here, right?
OK, looking good....
Turn your left shoulder down so that the imaginary club shaft points at the ball, keep the ball under your nose, let your right leg straighten a little bit to help your right hip turn out of the way...
...and THAT is stack and tilt! How easy was that? You practically nailed it already!

That drill itself DOESN'T ACTUALLY WORK AT ALL for the conventional swing, yet I've been doing it for years! The conventional swing (if you remember) necessitates a lean to the right with the spine and it turns away from the target. Well you just can't turn your shoulders properly with a club across your chest if you start with your shoulders tipped right, bent forward at the waist, and trying to keep that right knee flexed, it feels like you're completely pointing the wrong way, and even more so if you then try and move onto your right side... for arguments sake let's not even begin to add the golf club or swing plane into the equation!
I was sold. Stack and Tilt was for me. Provided I'm set up correctly I only need to worry about two things.. turn my shoulders down to the ball and let my right leg straighten as necessary. I can do that... and it's becoming more natural every time I play.