I haven't seen any mentions of MyLifeOrganized (MLO) for implementing GTD, so I thought I'd drop a post on ya. I futzed with a ton of software and paper implementations until settling on MLO. It's a VERY lightweight app. Works off a USB drive or full install and has lots of hot keys to add new projects, tasks, sub-tasks and has a wicked cool rapid entry dialog box that you can quickly dash off new thoughts into your digital GTD inbox. The niftiest feature is the "ToDo" list. I know, that's a dirty phrase in GTD land, but give 'em a break. You create your master outline holding your contexts, projects, tasks, sub-tasks and what not. Then you can define how long each item might take to do and you switch over to the ToDo list to see what you can do for your appropriate context. Have only 10 minutes? Filter down to see what can be done in 10 minutes.

Download the free version and mess around. It has most of the features of the standard and pro editions. They also have a pretty active board for MLO-specific issues with some GTD flavor here and there.

Product Page: http://www.mylifeorganized.net/products/my-life-organized/how-it-works.htm
Board: http://groups.google.com/group/myLifeOrganized