I very diligently logged my first 250 dives on paper. I wrote little narratives about them, and listed what species I saw. The day I passed Fundies, I drew flowers all over the page.
Nowadays, I log on the computer, and although I try to write some description of each dive, most don't get much. The program I use would permit me to upload photographs, but I'm too lazy. I do log each and every cave dive, with all the details I can remember or collect. And I write more about the memorable ones.
The biggest purpose of a dive log that I've found, aside from entertainment, is being able to go back and say, "What exposure protection and tank did I dive here, and how much weight did I end up needing?"