I've been reinstalling my P1i again (experimenting too much...). Next step is to sync it with my Mac. But there is a glitch with Sony's iSync plugin: connection lost with the phone when syncing for a first time. I think the problem is with amount of contacts you have in your Address Book. I have over 500 and it never worked for me straight away.

A small hint to deal with the situation: backup your Address Book (File -> Export -> Address Book Archive) then delete all the contacts in your Address Book (don't be scared, you have a backup). Sync your P1i again with empty Address Book. The process should go fine now. Right after that restore your Address Book archive (File -> Import -> Address Book Archive) and sync devices again. Here you go: all contacts transfered smoothly.

One more thing to get your syncing on track: Jonathan Furness' SE P1i iSync plugin which fixes the issues with calendar and to-do items. This one works like charm for me.

It's quite a shame for Sony Ericsson that it can't develop / maintain the plugin in a proper manner.