This item duplication situation has become a real problem for me. I have a whole bunch of people with dozens of duplicates in the iCal Calendars that I have published to them.
I have tried deleting all to-dos from both iCal and Mail and resetting iCal prefs in OmniFocus but all the duplicates come back when I match Contexts to Calendars in iCal Sync prefs in OF again.
I tried deleting the OmniFocus folder in my MobileMe iDisk online but that just wasted a whole lot of time getting sync connected again and the problem was there again immediately.
Can anyone tell me where I can delete all ToDos where they reside - in Apple's Sync Services and/or MobileMe?
Please help.

Hey watchit, this tends to happen when used in conjunction with a third-party sync solution. Is that possible here?

Hi derekr, MobileMe is sharing iCal ToDo data with Mail but I'm not sure if other apps are muscling in there. It seems to come and go. I've found that the only solution is to got through all of the ToDos I'm publishing from iCal and mark them as completed in iCal, then if they mark the Actions they're synced to in OF as completed then I go back and mark them as uncompleted in iCal and mark the duplicate as completed instead. This is a seriously laborious way of doing things but it is the only solution I've found so far. It would be so much easier if someone could tell me how to delete ALL of the iCal ToDos in Sync Services so I could start again simply by using OF's Sync with iCal command to send a fresh batch to iCal, then onto the published calendars. Any clues?