I tried countless times to get qtopia desktop to sync with mine (5500 w/ thekompany rom) with little success. I went back to OZ for that reason. KO/Pi works under both OZ and thekompany rom, so I figured I would rather use a rom with development potential, which it looks as though thekompany rom is stagnating a bit. Don't get me wrong, I liked thekompany rom, just not as much as I liked OZ.
If you haven't already, take a look at pi-sync.net. You can sync your Z's pim apps to the KDE-pim apps on a Linux box perfectly. At that point the only thing left is file sharing, which evidently can be accomplished with Samba, so Linux users are set.