I am a 4th Dan black belt instructor in Isshinryu karate, and I make this a part of my regular training routine. This is the second one that I have built, the first one that I built to a similar design having lasted in good condition through 5+ years or training. In fact, the only reason that I build this second version is so that I would have one that folds so I can put it in my car to take to class. The cost is very reasonable at $106.56 +tax (possibly a lot cheaper - see parts list), when compared to the $902 for a wooden dummy from www.Tigerclaw.com. The attached PDF gives dimensioned drawings of the wooden dummy, as well as multiple 3D views.
See below for a video of some of the drills that I use it for - you will see that it is very versatile. Also be sure to check out step 9 for extra features. I am planning on building several of these in the future that I can leave permanently at my school, so if you have any ideas for improvements please feel free to post.