I agree that most lessons end up being a waste of time. Lessons are often just 30 minutes - barely time for a "tip" or a "fix".
Everyone is to blame for this. Amateurs for their expectations of improvement from 1 30 minute lesson, pro's for their willingness to go along with that and offer a tip or fix. TV pundits for confusing everyone with their pet theories. Pro's who write books and DVD's that promote themselves and contradict each other. And finally amateurs again for not practicing enough, not practicing effectively and not having a consistent setup.
And I agree with iacas, many pro's are useless. Out of 7 pro's I have had lessons from over 8 years, 1 was only interested in selling me new clubs, 1 spent half of each lesson strapping me into all sorts of measurement gizmos and then confused the heck out of me with technicalities, 2 failed to find anything for me to work on "you have a nice looking swing, I can't see what the problem is", 1 was just using the video and trying to make me look like Ernie Els, 1 was able to come up with useful tips and fixes, and finally, 1 has made some fundamental improvement. So, my score would be 5 out of 7 stink (70+%), 1 was good for a tip or fix and 1 is good for developing a decent swing.
I think the important point here is to separate full swing ball striking improvement from everything else. A single lesson is OK, for example, if you want to improve your chipping, or if you have suddenly got "the lefts" and need someone to spot something that has crept into your game.
I agree with headgolffool that if you want to get the best score you can, most people would do better to avoid lessons on the full swing, and stick with what they have. They would do better to use smarter course management and improve some basic short game techniques.
If you want to improve ball striking, IMO, get ready for some serious effort and take the time to find a really good pro. It took Nick Faldo two years to re-model his swing. It has taken me 4 years (and counting) and I think I am just beginning to see some early signs of improvement now I have finally found a decent pro.
We need some unbiased, not for profit, advice for amateurs on how to learn. The advice needs to be far more specific than "consult your club pro", due to all of the above.
Here is an idea: if it has not already been done, why don't sandtrappers get together and write it?