Andrew Hyatt's blog mentions his merger of TM4SA's "The Cycle" with the GTD methodology.
I solved this problem by using the agenda, and scheduling my next actions that I wanted to work on for the current day. I would then see a list of the next actions I had to accomplish that day. If I didn't get them done that day, the next day I'd move them up a day, to the current day. It ended up being a daily-planner-like system a lot like Tom Limoncelli recommends in Time Management for System Administrators. But with next actions..Sounds great, Andrew!
I like GTD but don't think it is optimal for busy system administrators or software engineers. His addition to The Cycle is a great variation on the theme. That's how I hoped The Cycle would be used: a good system that people could adopt then customize for their own use.