I have noticed some interesting things in address-o-sync.
- Nowhere in their documentation does it list the port that needs to be added to the firewall to allow incoming connections. (I believe that port number 9879 is used)
- Only up to 4 email address for a contact get synchronized between computers. I wonder if this is caused because Apple's implementation of vcard only handles 4 email addresses. It looks like the vcard spec itself, doesn't have that limitation