Entourage 2008 allows you to turn on syncing. With this feature your contacts, calendar events and notes will sync with the same repository used by the System Address Book, iCal, and then iSync, iTunes and .Mac syncing.
The problem with this, very useful feature, is that it does not work correctly and in most of the times generates duplicates of your address book. I mean there are not only copies of your address entries, but there will be a couple of duplicates. Some reported that their address book, consisting of 400 addresses, grew to 30000 entries!
In this case, the best is to disable this functionality for now until the Mac Unit of Microsoft brings us a fix. For those with duplicates you can find a solution right here.
(reposting a post from Cortig.net) Jolly Roger posted a very useful script on microsoft.public.mac.office.entourage. The script finds and deletes duplicated events in the calendar (not discriminating what calendar they are from). The script is written for Entourage in English and you can find it on his site. You can install this script in your Entourage Script folder.
