Time zone rules change relatively frequently - future dates may be better stored in the appropriate time zone, optionally along with the UTC offset at the time

Time zone rules change relatively frequently - future dates may be better stored in the appropriate time zone, optionally along with the UTC offset at the time of recording, so you don't report incorrect information when the rules do change on you. Past dates should always be in UTC, for the same reason - timezone rule changes are sometimes even retroactive.