1. If the time zone changes (like, as it's happened multiple times in my country, the date for switching to daylight savings changes) you have to make sure all your servers is updated with the change
2. Daylight savings mean that events an hour apart can end up having the same timestamp.
I've fortunately never experienced (1), but for (2), it helps to print the offset to UTC everywhere timestamps are printed, even for UTC. (I basically never trust an "unzoned" timestamp.)
