I use Thunderbird as my email client in 3 different computers, and synchronizing the address book was a bit of a pain. Fortunately, there is a little add-on called Addressbooks Synchronizer that takes care of doing it automatically when the program is opened and closed.
This is accomplished by uploading and downloading the entire .mab file with the address book to a local or remote directory using FTP, HTTP or HTTPS or, more interestingly, to an IMAP folder. It’s not the most elegant solution in the world, but I’ll give it a try and see what happens.
Update (13/08/2007): After some testing, Addressbook Synchonizer seems to be corrupting my address book, adding garbage to the end of the abook.mab file, which makes it unreadable by Thunderbird.
