I checked the table structure behind piCal and here is a suggestion.

Instead of keeping all the events in one table you could use two. One for the event definition and another, much simpler, for the event occurence.

This could be very convenient for repeating events. Instead of having many copies of the same event you have only one row in the first table and then as many rows as needed in the second. This second table will basically have just dates. The relationship between the two tables would be one-to-many.

I can get into more details if you want...

Cheers,
Marius