hmm, interesting...
Mark/Space Users • View topic - iCal All Day Events = 8AM to 8PM on phone
Assume you are also running Leopard on the Mac. In these situations, would say make sure all the Time zone settings are correct first. Mac in the Date and Time pref pane. Also, in iCal > Preferences, turn on Time Zone support to verify the correct zone is set. Lastly verify the time zone setting on the BlackBerry.
If those are all set correctly and the problem remains, do a reset of Sync Services and then do a Mac overwrite sync one more time:
1. Go to iCal and click the 'File' menu and choose 'Back up iCal'
2. Now revert to the same database you just backed up, click on the 'File' menu and choose 'Restore iCal'
3. Do the same process for Address Book click the 'File' menu and choose 'Export - Address Book Archive'
4. Now revert to the same database you just backed up, click on the 'Import' menu and choose 'Address Book Archive'
Steps 1 through 4 are key to the process, they are not just a backup, but the revert part forces a reset of the relationship between Sync Services and iCal and Address Book.
5. Launch the iSync application, found in the /Applications/ folder. (iSync is not used for the sync, but iSync is where Apple handles Sync Services Preferences.)
6. Click on the iSync menu
7. Choose Preferences
8. Click the 'Reset Sync History' button. Read and follow the onscreen directions.
9. This may or may not launch iCal. When the reset process has begun the button will go grey, it is complete when the button becomes active again, but there is no need to re-click it.
10. Restart the Mac
11. Soft reset your BlackBerry. Turn it off, pull the battery for 3 minutes, put it back and turn on.
12. In Missing Sync for BlackBerry, double click the Calendar plugin and reselect the calendar for the field: "Put events created on the device into:"
13. In Missing Sync for BlackBerry, double click the Tasks plugin and reselect the calendar for the field: "Put Tasks created on the device into:"
Then, try the overwrite sync again.
p.s. There is also a setting in Missing Sync preferences to set the device clock on sync, that may be worth trying as well.