My roommate just made a bunch of screencasts on advanced Omnifocus features. For people who are unfamiliar with Omnifocus, it's a Mac app that heavily uses GTD features. If you search on this forum for Omnifocus you'll see that many people think it's one of the best GTD apps.
For those who use Omnifocus, I hope the screencasts are helpful and are of value to you. You can find them here:
Advanced Omnifocus Functionality
My roommate's approach to GTD is a little different (as you can see in the screencasts), but that's the great things about GTD that you can personalize very easily within the framework.
I hope you guys like it.