Apparently, these are well know problems with Entourage putting duplicates everywhere. There is even a FAQ topics on duplicates thanks to Joe for the pointer. Now maybe I can get rid of the 30 entries for St. Patricks Day in my calendar.
There is a simlar set of utilities of iCal that google:”ical duplicates” and [...]
Entourage and iCal Duplicate Removal
April 20th, 2008 · No Comments · Apple
Tags: Address Book·Amp·Applescripts·Calendar·Cocoa Application·Deduper·Entourage·Faq Topic·Google·Google Net·John Massey·Knowledgebase·Nav·Pointer·Simlar·St Patricks Day