Hi,
We (UNED) have been implemented a system of calendar's reminder recently. The idea is, as you have explained it, to notify users (personal or groups) of calendar events x days before.
Our exposition was: 1) to use the notifications when the events are added/modified. 2) A schedule procedure daily that checks the notifications and sends the corresponding reminders.
The code is available at http://cervero.innova.uned.es/dotLRN/calendar-reminder.tar.bz2 . I hope it will be useful for you.
As we are a few with the same need, it would be interested to work together on a common reminder solution and contribute it to community.
