On pda calendars:

There should be some way to account for travelling into different time zones
when creating appointments.
Maybe a new category called "travel".
A person's current location has a lot to do with what face-to-face
appointments can be scheduled.
If an alarm is tied to a scheduled event and you are not in your home
time zone, then it can get really bad: You won't be notified until after
you are late to the meeting, or maybe just get woken up for a meeting
depending on whether the new time zone is later or earlier.

If all events/appointments could be scheduled with timezone in mind,
then this would not be an issue.  And a travel event could automatically
adjust your clock's timezone.