I've been thinking of introducing a daily log into my GTD system but am not sure exactly how to go about it.

Why do I want a log? Isn't the beauty of GTD the ability to get stuff off your mind and out the door?

There are four reasons I'm interested in a log:

1) I want to assess my work habits/productivity during the weekly review. The action lists don't give me much clue about the order in which I do things or the amount of time it takes to get each thing done. The log would also help me become more aware of why I procrastinate on certain tasks. (Also useful for billing and tax purposes when I do freelance work.)

2) Research tracking. I want to be able to review my academic work to understand how I've gotten to where I'm at--to revisit dead ends, to understand my reading/research habits, etc.

3) Spending & health. To monitor my bad habits.

4) To have a "diary" of sorts. I might consider expanding the log to include brief notes about conversations, activities, observations, etc.

This all seems appealing, but I'm also wondering whether it's too much work on top of collecting, processing, and acting. It introduces another level of stuff to be aware of and record.

Also, I'm not sure whether to have a single log (simpler - single point of entry) or whether to divide this into multiple logs (spending, health, work, research).

Finally, I've gotten myself all confused at how a log relates to collection. In some ways, collecting is a log of thoughts. It's the input side of GTD--stuff that comes into my life that needs attention. But I would also like a running log of the "output" side of GTD--stuff that I do. It would be ideal to keep these two logs distinct. But separating them also introduces a whole new level of complexity into my system. (Right now, I'm all paper, using a hipster PDA.)

Any one have any success implementing a log? I'd be interested to hear any advice and/or suggestions. I'd prefer a paper-based solution, as I do much of my work away from the computer.