Sorry this has become a pissing match. I too am looking for info and the results of others. Here is my experience: the ladder has helped me to narrow down the field. It has helped me to find a powder that works well in the velocity range I desire.
One problem with the "method" is that it may not be good for the inexperienced shooter or for use in an unprooven rifle. (Please realize I'm not calling anyone out or saying my rifle is better than yours). That is to say, if you can not call your shots by the sight picture you have when the trigger breaks, this method may not work well for you. That leaves you wondering about the results. Looking at the target you may say "I prolly pulled that one". To use the method well, you must be able to account for each shot.
The method is not the end all be all, in my opinion, but it is a good place to start.
My reasoning for using it, I do a bit of longer range shooting, my intention is to find a powder that shoots well at a particular velocity, not just find an accurate load. Once I find that "sweet spot" I refine seating depth to zero in on the most accurate load I can find. I have tried running an additional ladder to determine seating depth but was limited by my optics, ie I could not determine which shot went where cause the groups were too small and beyond 300yds my spotting scope could not pick up the holes except under ideal conditions (which we all know dont happen when we want them to).
So the next trip to the range, I shoot groups of 4 at different seating depths. 4 is my magic number as I believe a 3 shot group is enough proof at this stage, but you never know when you may have an oops. I shoot, say to myself, "yea, that felt good", or "I think I pulled that one left and low" whatever, call the shot, then look through the spotting scope for proof.
Once I find the seating depth that seems best, I load up another 10 for the next trip for final proof. It usually takes me between 50 and 60 rounds to develop a load if the initial ladder provided accuracy in the velocity range I was looking for. Heres my results: