Hi! Elliot Murphy here. It seems I was overenthusiastic when sending that email to the couchdb dev list, and left out an important word: 'can' be replicated :)
Ubuntu 9.10 will have an address book in Evolution called "Ubuntu One". Users may choose to store contacts there, and other tools such as Macaco Contacts and Akonadi are integrating with the same data store. I hope this will enable some progress on a cross-desktop unified address book on Linux. Optionally, users may choose to subscribe to the Ubuntu One service, and replicate their files and contacts database to one.ubuntu.com. The service has a free plan with 2GB of storage space, so I consider that as being available to every singe Ubuntu user. It's totally optional though. At some point, we'll also be offering over-the-air syncing of the contacts in the cloud with your mobile phone, and I think round-trip syncing of contacts between your phone, your linux desktop, and the web is something that many people will enjoy.
If people don't want to use the cloud, thats totally understandable. I think some portion of the userbase will always want to avoid cloud services, preferring instead to keep all their data under their own direct control. One of the reasons I'm excited about using CouchDB for this system is that at last we don't have to force people to choose between replicated convenience and maintaining total control over their data. It's also easy for a user to set up peer-to-peer replication of their CouchDB to their own machines without going through Canonical servers at all. There is even a little GUI tool to make this easier in the desktopcouch-tools package.
Sorry to have alarmed people, I hope this explains things a bit better. I'm always interested in hearing feedback about how to make the design better, and I'm very passionate about designing cloud services that provides much more user autonomy than the current common practice, while also providing a lot of user convenience that makes so many cloud services appealing. The ubuntuone-users mailing list is a great place to send feedback, and can be found here: https://launchpad.net/~ubuntuone-users