I used to use a bunch of todo.txts, but then I wrote a system that allows you to basically enter todo.txts online, parses and categorizes them, while keeping original text nearby. And it's available wherever you are. The original problem I had with all the other GTD systems was a lot of tabbing, I type around 120WPM and it's much easier for me to enter something like:
project taskulus.reliability.history.milestone36
1. cleanup scheme:30min
2. add observed_in_task field and test:30min
3. add HTML generator for event history:1hr
It's basically like microtasking :)