I wanted to share an experience with you I made during the first couple of days using the new Apple iSync 1.2.1.
I didn't get it to work properly until I switched off the "Auto-Start" and "treat as System application" option of HandyDay (I'm using version 4.1). Also, a friend of mine also mentioned that HandyDates seemed to have caused problems.
After switching off these options, make sure you close all applications e.g. using HandyDay's built-in TaskManager - especially, make sure you close HD.
Symptoms were two-fold: either no connection could be obtained with iSync or an internal HandyDay crash followed by a Kernel crash of the P800 during syncing. Actually, the second one got me thinking.
I'm now happily synchronizing my P800 with Apple's apps, my .Mac account and with MS Outlook on my PC. With some minor quirks, but it works.