Since restoring my iMac from backup, every time I try to sync my iMac and my Treo, it says something along the lines of, "Syncing with phone will change more than 5% of your Calendars on this computer. Add: 1158. Delete: 0. Modify: 3. Ok?" And sure enough, if I say "Ok" it duplicates every event in my iCal. Each time.
I think I want to just tell the computer, "blow away what's on the Palm and treat what's on the computer's copy as the ultimate authority." How do I do that?
Update: "iSync / Devices / Reset All Devices" sounded promising, but it just caused the Treo to start rebooting every time it tried to sync the calendar. So I did a memory-wiping hard-reset of the device (hold down Off for ~10 seconds while pressing the reset button by the battery) and that let it reinstall everything. (Except that for some reason, Snapper Mail made me re-enter my account info). So, it's fixed now... for now.
Update 2: The new version of Missing Sync is out now, and comes with its own conduit that fixes most of the complaints I had about fields not being synchronized. To get it to install I had to go through the "reset the device, reinstall Snapper" dance again, but now there's a lot more data in my phone's address book and calendar, which is very nice.