What I love is the people who go on ScubaBoard and write something like the following: "New divers don't learn crap in their OW classes. They look terrible in the water, with bad trim, incorrect weighting, and poor kicking technique. They should not waste time on more advanced instruction, though. They should instead go out and dive with that bad trim, incorrect weighting, and poor kicking technique until they have it mastered."
The question how practice vs. formal training should be distributed in time relative to each other is very interesting on its own. A number of people here pointed out that training, or at least mentoring, should come first, so that we have an understanding what to practice, what mistakes we make, and a solid reference point to measure our skills against. Of course, we all probably agree on that, at least I do. With this said, there are still a number of interesting questions that arise...
For example, how much practice does it make sense after training? As time passes by, our memory fades... we might slip into the bad old habits without knowing, or our carefully developed routine might begin to slowly degrade. Even if we know exactly how to practice the day after a class, at some point we might end up practicing it wrong... Should we try to get our skills assessed by a skilled fellow diver? Have someone videotape our performance during drills, or even just a regular dive? How many people actually invest in doing these periodic reality checks, to reassess where they are, whether they have regressed? How quickly do the various types of skills degrade?