I tried using a voice activated recorder but I found it hard to sit down and transfer my babbling into useful readable information. I also found that I wasn't very aware of which details I was noting and thus didn't always record all the information I could have used.

I now use a small memo book, which fits into the pocket on my camera bag.

Here's a short sample of what I write:

Kodak Gold 100
Louisville Swamp
1:46 PM

Clear skies, bright sun, no haze. 29-100mm

Twin Trees - trees are roughly 30' apart. @50mm
27) 250 f/11 (noted the angle of the sun in relation to the subject)
28) 250 f/11 warming filter
29) 45 f/11 warming polarizer
30) 250 f/5.6 warming polarizer

Twin Trees - second set. Trees are roughly 10' apart. @50mm
31) 250 f/5.6 wm pl
I keep these notes on one side of the page only so that on that on the facing page I can make any other notes I feel are necessary. Such as how I found the spot or other subjects I might want to go back and shoot at another time (under different conditions). It seems like a hassle to stop and make note of what you're doing but I have found that I am taking a lot more time to take the photos as well and there may be a payoff in the end for that.