[Felz]

We do have CardDAV support, and hope to develop CalDAV soon :)

[brongondwana]

Good luck with CalDAV - it's pretty hairy! I do recommend joining CalConnect if you have the budget for it - you get access to a lot of experts there. Or at least show up to the calsify mailing list at IETF, we're pretty friendly there too. The edge cases in Calendaring are a right pain.

[malinens]

I would recommend using some existing opensource tool for that and not roll your own implementation