I keep a log book / journal. I used to be religious about it, but now I probably only capture 70%.
I find it most useful when I can't decide what kite to put up on a particular day based on the wind and water conditions. I can flip back in my log book and look for similar weather and then read comments regarding if I wish I'd had a bigger kite or was perfectly powered, etc.
Comes in useful.
How many times have you assessed the wind conditions, chosen a kite, and then someone else comes by and tells you are rigging too big or too small...you change your kite, go out, and wish you'd stuck with your instincts on what was right for you? The journal helps me. Or, if you just had a good memory I guess you don't need it.
Anyway, good to know other kiters do this also! I had gotten the idea from watching backcountry ski guides. They assess the snow/weather/group conditions at the top of each run and then summarize after how it went. Helps them learn to read the snowpack better and recall what worked on particular days and with particular types of groups.