I've often wondered how much people really gained from instructors. I often here great raves from a player after an instructor session, but it always seems their playing ability doesn't change much. They seem to stay at the same speed...3 or 6 months after their lesson.
I wonder how often is it the 'placebo' effect that occurs right after a lesson???
There is one thing about getting lessons that a lot of people seem to ignore. People actually have to PRACTICE what they learn lol. So many people go to take a lesson and think an instructor is going to give them a magic pill to make them play better, and its just not out there.
The strength of a good instructor is often in their observation skills, and being able to point out what it is that needs to be changed. Most players do not have the discipline to stop playing long enough to work on these changes. It is very hard to change mechanics, especially if you are "playing" while trying to change. When we start playing we normally revert back to what we were doing before, unless we have spent enough time solidifying the change. Even then you have to have a good understanding of what your bad habits are, then you know what to look at first when your game starts to go off track.