Rated 3 out of 5 stars
this is a great addon (when it works). It allows simple set-and-forget contact and calendar sharing on multiple machines (even when both are running, which is impossible using shared network folders).
I've gotten it to work fine with addresses, but it always hangs when trying to sync calendars (using lightning). Once that bug gets sorted, you can even use it as a cheap groupware solution (like sharing a calendar with friends) as long as everybody has access to the same IMAP account.