There is this annoying bug in Leopard's iCal called the "calendar cache" bug or the "stuck" bug. It's an issue with iCalendar feeds. Sometimes when an event is edited or modified in an iCalendar feed, Apple iCal doesn't properly update the event.
This is a problem for many web based applications (like Heap CRM) that provide iCalendar feeds. The reason this is sometimes called the "calendar cache" bug is because this problem is all about the "calendar cache." Apple iCal has cached the event, it just doesn't think there is any reason to look to see if it has been updated. By simply deleting the calendar calendar cache, it forces iCal to update the event.
Obviously, to delete the calendar cache on a regular schedule by hand makes no practical sense. So I wrote what I have to assume is simplest Automator script ever written.
I also have this saved as an application, so that I can run it in the background. What I personally do is have the application run every time I login. So at least once a day the iCal feeds are forced to update. You can run it as many times as you like, or assign it to a schedule.