in reply to Work practices: log books, notes files...
I have long done something similar, though not quite to the same extent. I don't save every command, just ones I feel relevant or wish to repeat combinations of. In addition to dated text files such as yyyymmdd.sql, I have also used a single file wikis like GTD Tiddly Wiki Plus to make it easier to organize notes by project. Here is the 43 folders description page and a direct link. It provides an easy way to keep things organized and is easy to carry around on a USB memory stick.