I finally have all of my contacts synced across all of my systems but it was a painful process, and I'm not real confident that future updates are going to sync correctly.
I had to first unregister all of my systems from MobileMe. Then on my main Mac I had to start the iSync app, go to preferences, and click "Reset Sync History." Then in the MobileMe prefs panel I re-registered the Mac, then synced, telling it to replace cloud data with data from the Mac. That updated the cloud correctly.
On my other systems I had to again Reset Sync History from the iSync app, start Address Book and delete all entries, then go to the MobileMe prefs panel, re-register and sync, telling it to replace the computer's data from the cloud. Finally all of the contacts made it across. Whew.
I'll see in the coming days if updates and additions get synced correctly. But I'm afraid I may have to go through this byzantine procedure if I really want all the data to be correctly synced.
Now that you have all you data in MobileMe Cloud/Servers (the Master File) then you should always be able to Reset you client(s) if needed. Assuming the Master File does not get corrupted.
With everybody having so many problems I have been running my MobileMe Preferences in Manually Mode for Contacts and Calendar (even though I have not been having any problems). I don't change them that often so it has not been that big a deal to just do a Manual Sync every so often. I plan to go back to Automatic Sync when it appears to be more solid.