The problem with 1 on 1 coaching is people expect it to be a quick fix. They rationalize "i'm paying good money for this, this guy is helping me one on one, this will make me a good player." You need to actively try to improve your game on your own, not just listen to someone telling you what to do.
This is why the training sites are better for the novice to intermediate player. You can get top quality instruction very affordably, and you are forced to actually think about what is going on, rather than just being told what you are doing wrong (rather, you are watching someone else play and explain, but it isn't jsut someone telling you yourself what your mistakes are). After watching tens to hundreds of videos and studying your own game, you should start to get a general idea of leaks in your game and see some results.
Let's say you are a winner at 2-4nl or 3-6nl and want to move up -- this moight be a good time to get coaching. However, I suspect most of the people asking questions on this forum aren't in this situation.
Also, one other thing for coaching. Please be very careful who you get lessons from. The training sites in this forum are all reputable companies that hire very good poker players with proven results (if you don't see proven results, ask). They have a lot to lose by hiring instructors who can't win. A lot of the private coaches may not have the same results or a reputation to protect, so you can get burned. I've heard of many many instances where people have gotten burned, even "coaches" who have gone broke, and took up coaching to get money.
BTW, there are lots of good coaches out there too. I recommend checking out
www.3-bet.net for good coaches. I don't know much about other poker coaching sites but they have a very good one.
tc