I started learning the Practical Method from video in February of this year (2011). Because I had studied Chen Style Taijiquan since 2006 and did not have a Practical Method teacher in my area, I thought I could learn from the wealth of information and videos available on the Practical Method website.
My first videos were the Basic Foundations and Yilu (First Routine) Detailed Instructions. I have since bought the Energy Alignment videos and various Mini Lessons. I also recommend Yilu Corrections.
Everything I have read and watched has been very useful. The instructions enabled me to quickly learn the choreography of and helped me understand some of the details of the Practical Method.
All this is well and good. However, it is one thing to watch the examples of the Practical Method in a video. It is completely enlightening to feel the examples applied to your own body.
I felt that it was important to go to a seminar to physically validate what I understood from the videos. I quickly found out that I made the correct decision. During the Edmonton week long seminar Master Chen manipulated and aligned my posture in such a way that I had a stronger structure. Naturally, it is up to me to continue to practice and work towards those ideals, so I can create the structure myself.
During the seminar there were many things covered directly and indirectly that I had learned from the videos or the information provided on practicalmethod.com. There were additional discussions that added to my understanding and gave me a path to follow and improve.
I used to think that you can learn Taijiquan on your own. However, it has taken many generations to get to this point. Each generation has transfered their learning to the next to continue and improve. This transmission is essential to learning Taijiquan. I now believe that I cannot learn it on my own.
The videos were an excellent start. If that is all you have, do it. Follow them and learn. But also know that you will need a qualified teacher at some point to show you how to really move and demonstrate the depth of learning that is possible.