I don't port too often but when I do I have been adding them to a spreadsheet. Their name, current location when asking for the port, current location at the time of the port, my location when they asked, and the amount they gave. I do this to determine the distance we each traveled to make the port happen and put down a travel time rating. 0 if they were next to me, 1 if I had to port to a spire where they are, 2 if I had to port then run for a couple minutes, etc.
I don't really have a specific reason for it yet, just collecting data :P I also think there is a big difference in someone only handing me 10 or 20p after I spent 20 minutes getting to them, and 10 or 20p when someone joins a port I'm already making or when I was already next to them when they asked at a spire. Convenience of the person doing a service for you should always be considered. You don't need to hand me 100p if I was already standing next to you. But you had me go from EC to City of Mist, then 100+ would be nice.
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But you can just do something similar to that. Then with the magic of excel formulas you can find out your total plat earned from ports, average per port, average plat with distance considered (and level if you track it... but if they are /role or /anon are you going to ask their level every time?), etc and they keep updating with every new entry.