In his recent Productivity Principles newsletter -- only available via email -- David Allen* describes his system and the response he has to people who ask "how long does it take?" and who are really attempting to evaluate the worth of the investment to learn something new.
What I'm going to say is going to sound either like the most egotistical or the most humble response to that declaration. It's not MY system, it's THE system. Actually it's a systematic process, not a system. All the stuff that we teach and coach is based on one simple premise: if something means something to you, then manage to deal with it the most efficient and effective way.
I really like this. All of the time management and productivity classes in the world teach some useful principles and give you some techniques for working with your favorite tools, whether they are paper, electronic or scratches on the wall. None of these will work if the activities you are planning is not meaningful or important to you.
* David Allen is the author of Getting Things Done, a book and a "way of life" geared around effectively accomplishing your work (seminars, newsletters, more books). The newsletter is free and registration is on the website.