Respecting time zones!
This is something I found lacking in all of playback statistics tools I’ve ever used. I’m not sure if it’s that much of a hassle to append time zone info to unix timestamps (like last.fm uses), not to mention ridiculously long LDAP timestamps (like in foobar2000). But in the end this kind of information doesn’t even need to be recorded with every single listen, because humans don’t teleport between different timezones yet. So it could be settled with ranges - all listens between dates X and Y were recorded in the time zone Z.
I think it’s really, really important for data integrity because people sometimes travel around the world and change time zones. So if I live in France for a few months during winter (UTC+01:00) listetning to music in the evenings, and then move to Singapore (UTC+08:00), I want my French listens to still point to evenings and not suddenly move to middle of the nights, just because my system clock is now in a different tz!
Recording listening stats with only UTC timestamps (no matter how accurate the format) means actually losing data, because fixed points in time require fixed location info.