I use the printed form method, of my own design, but based roughly on that which AA outlined in the negative. One day I'll put a copy online somewhere.
I keep every possible bit of data, and it really helps out. It especially helps me with remembering stuff, like reminding me to factor in reciprocity correction for that fleeting night shot which I'm rushing to get.
Once I get home, this info, along with development info, goes into an MS Access database, though I'm thinking of moving it over to a MySQL-based system, so I can access it from anywhere.