I’ve also used DT and Gnomon Workshop and agree that both are good resources.
For me DT is a good starting point for learning the basics and technical aspects of using software. Gnomon I feel touches more on the artistic side which is great. I think what you get out of a Gnomon tutorial is really going to depend on the instructor. I agree that Scott Spencer is a good one. Watched his DVD’s and took a couple of his online courses at Gnomon and he’s a solid instructor. If you want more from him, get his Zbrush Human Anatomy book at Amazon. It’s a great book with an even better companion DVD that’s essentially a Gnomon DVD itself with very detailed tutorials.
While DT is great for beginners I tend to think that Gnomon is better suited for those with some experience. Not to say GW doesn’t have good beginner stuff, but you may be better off knowing the basics because some tutorials tackle some crazy stuff.
From the GW tut’s I’ve seen, they rarely speed up the demo. But I do find that many obviously do the work first and then come back and overlay their dialogue afterwards. But I’ve never found it to be a problem.
Overall GW is pretty good at showing you their techniques. Particularly the Josh Herman tut with the Silver Surfer you referenced before.
The only knock with GW, is that despite the library as a whole, for the price, they just don’t come out with new titles often enough. The library is also fairly focused on the subject matter whereas DT is much more broad.
But both are certainly great resources for learning. 