After Bryan's big-picture questions, I'm a little embarrassed to post my decidedly small-picture one, but after being "on" GTD for a couple of years now, I still haven't found a really satisfactory way of dealing with recurring tasks/chores that aren't tied to specific dates. Things like changing the air filters, or working on various personal development projects that I don't have time to do every day but want to maintain with some regularity.

There's a Mac app whose name escapes me right now that's designed to handle this sort of thing, but it's overpriced and didn't seem to integrate well with the rest of my system(s) when I (briefly) tried it. What I do now is maintain daily, weekly, monthly etc. "Routine" lists that I keep moving forward in my tickler file, but that's a little too fiddly even without breaking out the individual tasks to separate sheets.

So I'd ask David if he's dealt with these sorts of tasks in his work -- surely he has, but he doesn't seem to address them in the books -- and what recommendations he has.