I must be one of the lucky ones!
I just synched my 8100 for the third time, address book and iCal only, and all addresses updated in BOTH directions and iCal also updated in both directions. I set both for a "two-way" sync.
I know there are MANY who are having trouble with PM 4.0 and Macs, and I was VERY scared to use PM (I backed up my address book and iCal before the 1st sync), but it has been working so far.
One idea... I did have the dreaded "not enough USB power" error the 1st time I tried to sync, and I DID have some issues with disconnecting and non-sync UNTIL I plugged the Pearl into a POWERED USB HUB!! THAT seems to make a BIG difference!