UTC is generally a good idea for storing, but there are still some ways to have that bite you. If a user enters a local date time for a future event in a particular time zone, converting that to UTC could result in incorrect behavior if the timezone definition changes. It depends on if the user meant that UTC time or if they meant the local time.
It can also cause trouble if you store past events but do not store the user's local offset or timezone at the time of the event. If you aggregate these events later into a dataset of "events by hour", they may be grouped wrong (from a user's perspective) if you convert them all to the user's _current_ timezone.
