Full ACK. I'm managing my GTD with orgmode for about 2 years now and I'm absolutely satisfied with it.
The biggest advantage of orgmode is the fact, that all is just plain text, so I can manage tasks just with the keyboard instead of point&click into dialog boxes. This speeds up the process a lot.
Speed is important for your task management tool. In the firm we're forced to also use SharePoint-based task lists and here you really see the difference between just editing a text file in your PCs RAM or suffering from a lousy responding server that makes editing a task a long job.
Ok, the big differenc is that orgmode is not a "groupware" tool, its for self management and for that its perfectly suited.