I use the flight log program listed above, I like it alot, I have my laptop at the field, I jot down notes and then when the Rx battery needs a charge, or for whatever reason I'm just gonna stay on the ground for a bit I'll enter it in, sometimes.  Other times I'll just do it when I get home, I don't worry that much about missing anything but it is nice to get general trends, and to detect early problems (comparing settings and trims and things, being different than normal, etc.)