Here's a bit of trivia for those wanting to move their entire Address Book from one Mac to another: Copying the files under: ~/Library/Application\ Support/AddressBook across just works. The Images folder inside contains the contact images, the image filenames being the unique ID of each contact.
The same thing works for calendar data (just copy the calendars across - you'll find them in ~/Library/Calendars, which makes Address Book look a bit inconsistent - why not have ~/Library/AddressBook as well?).
For permanent syncing, I'm considering adopting this hint instead of using .Mac for syncing calendars and to-dos (it's a bit pointless to shuffle bits across the entire Internet to get from one Mac to another), with the added bonus that there are a lot of PHP front-ends available to view the published data from anywhere.
As to Address Book syncing, I'm still fidding with Projects/vcard2ldap. At the moment, one of my gripes with Address Book is that it doesn't save contact photos when exporting to vCards, and that some of its choices of fields when exporting "extra" data (i.e., optional phone numbers and addresses) seem to be non-standard. But hey, at least I can actually get at the data...