I definately log all my dives. Im a new diver.....really havent done any REAL dives yet. Just my training dives and a specialty dive. I love marking everything down in my logbook (a padi cordura binder). If theres a space for information.....I fill it in!! In the notes section I will note what fish I saw, if I was cold, how I felt about my weighting, how smooth the dive went, etc. I try to record all information so that a stranger reading it will know exactly what kind of dive I had.
I have a Suunto Cobra computer which pretty records everything for me, which I download to my PC. It records depth, air usage, bottom time, air temp, water temperature, time in, time out, etc. It allows me to place bookmarks in a dive profile and then annotate it later on my pc. For example the dive manager software will produce a graph which represents the dive profile in depth and time. If I see a shark at 54fsw I can push a button on the cobra to bookmark it. When I open the graph on the PC, there will be a mark at the 54 foot level which I can add text that says "saw shark" or whatever.
With the computer log, I have to add information it wouldnt otherwise know like: where the dive occurred; what size tank was I using, who was my dive buddy, my notes, gear I was wearing, etc. But you can create virtual "gear bags" to pick and choose from which makes this really easy.
I like it mostly because it automatically records information for me so I dont have to focus on it so much during the actual dive. I can always come back and get it later. It figures my SAC rate automatically too which is just way cool.
I keep both my logbooks current....paper and pc!!