My Uwatec computer is AI, so it does 90% of the work for me. Plus, it beams the logs over infrared to software in my Treo, which I bring with me on all but the smallest boats (in a pelican box of course). In between dives, I fill in the blanks: buddy name, size tank used (needed for the AI software to determine SAC), visibility, any interesting critters that I didn't take photos of, anything else of note, etc., using the little keyboard on the Treo.
I generally dive the exact same gear setup, since I own all my gear and usually dive locally, but if anything changes I'll not that, like wet or dry, how much weight, what thickness of wetsuit, etc., so I can dial in all my settings for future use. If I was underweighted, etc. I'll note that too. This way, next time I dive a jacket BC in a caribbean shorty using an aluminum 80, I'll know how much weight to bring, and when I'm in cold water switching between wet and dry suits, using a faber HP100 tank vs. a Worthington hp130, I'll likewise know how much weight to pull off or add onto my belt.
Later, as I go through my dive photos, I'll supplement the "critters seen" in the logs.
I'll also note what boat I'm on and if there is anything noteworthy there, or which shore entry location I'm using if beach diving.
Realistically, it only takes about a minute per dive, depending on how many critters I saw, because most of my diving is done under pretty similar conditions so a lot carries forward, and simple changes are picked off picklists in the AquaDiveLog software on the Treo.
Every few weeks, I import the ADL records into the SmartTrak software on my PC to complete the cycle, and sometimes add in a bit more info with the options available to me in the more full-featured software.
One of these days I'll print it all out onto log sheets of somesort and put together a portable book for long-distance travel, but meanwhile I always have my phone with me so it's very easy to look up a little bit of trivia (who was I with last time I dove Catalina, and on which boat?) in a heartbeat. And since it's all backed up in multiple locations (dive computer to phone software, phone software to desktop computer, desktop computer to backup disks, phone software to computer software, computer software to backup disks), the changes of ever losing everything are extremely slim... far lower than if I was using paper log books.