A dive log serves many purposes. It can be simply a "memory jogger" to help us remember gear configurations for a certain set of diving circumstances. It could help us to recall details about special places so we can "remember" to dive there again or even warn us against doing so. It could help us to recall why we don't want to dive with a particular partner again, or encourage us to dive with someone who is well suited to our styles and ideology.
For me, a dive log is a learning tool. It provides details that might otherwise be lost if I were to depend upon memory alone. I log all dives, some more completely than others, but I learn something from every dive I make, so I record it. Like H2Andy, my first dive was a "resort course". Did I learn anything? You bet! I learned that I definitely wanted to pursue this sport, and I resolved to find a dive center the day I got back home from vacation.
I just recently made a dive that lasted only 15 minutes and never got deeper than ten feet. Did I log it? I certainly did. My buddy and I were searching for a man's lost dental work ($2500 worth of porcelain teeth and bridgework) in a very murky lake. Visibility was only a foot. Did we learn anything and was it a memorable experience? Yes to both, so I logged it. By the way, would you believe we actually FOUND the missing dental work? It was a needle in a haystack situation, but our SAR was a success, so it's a terrific log entry.
Have fun, and it's your log...enter what you want.