Quick hacks aside, remember to think about timezones.
Do notifications go out as per the system timezone, or as per a user preference timezone? Consider the following scenarios:
1/ two users, in different timezones, have personal calendars with reminders - the reminders should fire as per their own timezone
2/ the same users are both in a conference call based off a shared calendar - the reminder should fire as per the calendar time zone
3/ the same users have a "weekly friday meeting at 8am" reminder in a shared calendar, they both should be reminded at 8am in their own timezone.
2 & 3 are difficult to achieve at the same time with a simple easy to understand ui.
there are even more difficult permutations when you sync to a palm pilot, and subsequently fly to a different timezone.
There is no perfect solution, but the final feature set will need to include some level of timezone understanding.
