I've been using Entourage (2004) for several years now, but I've gotten increasingly frustrated with how it syncs with iCal.
I seem to get a lot of duplicated events, for whatever reason. I'll delete the duplicates and think everything's OK, and then at some point down the road, I will once again have four or five copies of someone's birthday in the calendar.
So I'm thinking about just turning off the link between Entourage and Sync Services (at least for the calendars) and using iCal exclusively. I don't seem to have these syncing problems with contacts, FWIW.