I have enjoyed reading the various articles on the Dexterity developer site, but the Power of Clarity (http://www.dexterity.com/articles/power-of-clarity.htm) piece has left me in a bit of a quandary. As a project manager I can surely appreciate the importance of measurable success criteria. But simply having a goal is not enough; one must also know good ways to seek that goal.

First, you must decide exactly what it is you want to accomplish. Most people never do that in their entire lives. And secondly, you must determine what price you'll have to pay to get it, and then resolve to pay that price.
--Bunker Hunt

Now, perhaps I'm just dense, but this sounds vaguely reminiscent of the Underpants Gnomes from South Park. Phase One: Collect Underpants. Phase Three: Profit! What is phase two?

Having a clearly defined goal means that you can state the difference between where you are now and where you intend to be at some specific point in the future. As Steve analogizes in the article, "I will be at the top of the Eiffel Tower" is a goal. However, if I am standing in the middle of an avocado grove in southern California, I may not know how to get to the Eiffel Tower. I could walk in any of 360 different directions and never reach Paris.

Since this hypothetical goal is geographic in nature, I could consult a map or hire a travel agent to guide me and have some assurance of success. But if my goal is "to double my present income in five years," I would be hard-pressed to evaluate the wealth of available advice.

Simply put, how does one go about deriving a plan from a clearly stated goal in the business world?

You're correct that goal setting is only the beginning, and by itself it's not enough. There's another article on this site about planning that may be of use to you:
http://www.dexterity.com/articles/planning.htm

For virtually any complex long-term goal you set, there will be limitless ways to get there. As human beings our plans will seldom be optimal. We never have perfect knowledge, so perfect plans are out of the question. This is why it's often very helpful to break larger objectives into smaller ones that will help move you in that direction.

There are many techniques for planning and solving problems. Modeling is a one we all use a lot: Find someone who has already solved a similar problem, and copy their solution. For example, if you know someone who's been to the Eiffel Tower, find out how they got there, and do the same. If your goal is to double your income, you could also find someone who's done this and ask how they did it. Years ago I met a man who grew his business (not software related) from $40K/year to $400K/year in just two years. I asked him how he did it, and he gave me some general advice which sounded dumb and obvious to me. But when I applied it, I doubled my income in about six months. His advice was simply to learn what caused previous income increases in my business and do more of those things, and learn what caused income decreases and do less of those things (or prevent them from occurring). Sounds obvious, but it helped me focus on what really made a difference, and I reprioritized products as a result.

Planning is an iterative process. Planning is simply the process of answering the question, "What's the best use of my time right now that will allow me to achieve goal X?" You will never answer this question perfectly. But if you do answer it and then take action on your answer, you will get results. Whether your results are good or bad, you will learn something. And based on what you learn, you will answer that question differently in the future. Thus, your plans, actions, and results will be constantly changing. It's the "read, fire, aim" approach. For example, you may decide to reach Paris by walking. But when you evaluate your results, you'll quickly learn it's a bad idea and try something else. By trial and error, you'll eventually figure it out. This is the slow method of learning, but as previously mentioned, modeling someone else who's already succeeded is a way to speed up the learning process, since you'll learn from others' mistakes.

Keep in mind that the future is something of an illusion. You never exist in the future, only in the present. If you create a monolithic long-term plan, reality will corrupt it very quickly; it will always be inaccurate. Plans are only valid to the extent that they tell you what to do NOW -- in this present moment. So you only need to plan as much as necessary to gain clarity about what you should be doing now. If you already know what to do now, then you don't need to plan... just take action on what you already know. When actions become foggy and uncertain, it's time for more planning.