I have a distinct preference for keeping my Mac OS X Address Book local as I sync it between two Macs. There are several ways to do that, and the method I chose had a peculiar problem. I finally figured out a fix.
Back when Mac OS X was using sync services, before MobileMe, I had a problem syncing the master Address Book on the Power Mac G5 to the MacBook Pro. No matter what I did, new entries and changes in the master (source) would not make it into the slave (target) Address Book. So I gave up on that technique.
Later, I tried the process of exporting the address book on the PMG5 and then importing it into the MBP. You get to name this archive file, and its extension is .abbu (Address Book Back Up).
Address Book can Export an Archive Manually
Importing that archive file on the target Mac had the same, failed result, so, for some time, my address books were out of sync.
Exploring the Possibilities
One idea I had, and Bob LeVitus agreed, was that the source address book might have become corrupted somehow. Moreover, a friend of mine back in the Apple days had a habit of writing a virtual novella in his Address Book Notes field, then he'd e-mail the vCard to me. I suspected that these very long notes might be a problem. But how to look for genuine corruption remained a problem.
Then I remembered, from a long time ago, that there is an Address Book exporter. I found it again at http://www.antoniolore.net/. This handy utility exports the entire Address Book as a Comma Separated Values (CSV) file suitable for importing and inspection in Excel or Numbers. So that's what I did.
I stretched out the columns in Numbers and looked for odd looking data in 762 entries, but didn't find anything unusual. I did use Numbers to quickly identify, visually, those entries that had very long notes. (And I mean long.) However, since the export is one-way, I had to go back to the Address Book to do the actual deletion.
I used normal Apple File Sharing and brought the exported file over to the MacBook Pro and tried an import. No luck. None of the new entries and changes showed up. I quit Address Book in disgust.
I've been spending a lot of time lately roaming around the Application Support directory. /Users/your_acct_name/Library/Application Support. On a hunch, I deleted all the files and directories I found in the AddressBook directory and re-launched Address Book. As expected, it had the default entries, the same as when Mac OS X is first installed.
This time, when I imported the .abbu file, it worked. So far as I could tell, the imported Address Book entries were identical and the count of cards (entries) matched.
First Order Check for Good Sync: Card Count
What this tells me is that Apple still has some issues to work out on the Mac OS X side of MobileMe. I don't see how MobileMe can expect to work flawlessly when this kind of issue can keep an Address Book from syncing properly when it's done manually. It's certainly not the kind of thing one would hope to encounter as a newbie to Mac OS X, but for those who do have a problem, the techniques described here might help some day.
Accordingly, my plan right now is to switch to MobileMe in 2012.