Nothing new to add really, but that never stops me.
Like others I use a GPS, in my case a handheld which I plug directly into my computer to make a copy of the track log. This records start time, speeds and of course location - all of which can be viewed on the chart on the computer.
I then keep a spreadsheet, one per boat we have ever owned, which has all the important bits.
On board I use a waterproof notepad to keep a record of anything I might like to recall later.
When I have had a cabin boat then I have kept a more wordy log, with maintenance issues and things like that all written up.