Personally, I have a laptop that stays in with my reptiles running Degei. I can just click the change/update as I go. It allows me to track where the snake came from, goes to, and in between.
Also inventories the feeder rats as I feed them, so I don't have to worry about counting stock for every time I ponder "do I need to order, and what."
Has many other features, like ID cards and useful reports.
I used to do cards and notebooks, but found this to be a touch slower, but easier still. Also saves having record and paper everywhere and needing filing.
The one concern has always been if it craps out on me, what then? This is one advantage to hard copies... so I wrote a .BAT file which backs everything up so I can just reload on another comp if that one fails.