TreeSync is proving problematic. In short, if your FTM database needs to be restored, you can't use TreeSync with your ancestry.com tree any more.
I had been looking forward to it because my ancestry.com tree had gotten stale; it was too much trouble to duplicate all my changes to my FTM tree in my ancestry.com tree. Automatic synchronization sounded great. It was easy to set up. Pictures took a day or more to catch up, and it wasn't findable in searches for a week or more, but it looked like a good way to go.
One day, I exited FTM after making a number of changes. As expected, it began to synchronize with ancestry.com. The synch suddenly stopped with a generic error message, and then FTM crashed. When I restarted FTM, it couldn't open my database. I could navigate to it and select it, but FTM would simply fail to open it, without explanation. It kept going to the screen you get when you're starting from scratch with no data.
I had a backup, but it was a few weeks old and I had made quite a few changes since then (of course). I was able to restore it successfully, but this left me with a dilemma.
The ancestry.com tree still said it was using TreeSync. It turns out that it would accept nothing but the database that created it. According to support, there was no way to have my restored database and the ancestry.com tree resynch with each other.
I could either try to remember all the changes I had made since the backup and redo them, and then create yet another tree at ancestry.com for TreeSync, or I could download from ancestry.com into a new database and keep the synchronization. Neither alternative was ideal.
There were two problems with using the restored database. First, I might not remember all the changes I had made. (An automatic change log would have been useful.) Second, my public tree was already being searched and used by others. Creating a new tree at ancestry.com would mean my current tree would become stale, not receiving any further updates, and there'd be no way to direct people to the new tree.
I downloaded from ancestry.com, but there are (so far) two problems with that. As noted in knowledge base article 5356, not everything transfers between FTM and ancestry.com. If you uploaded your FTM database to ancestry.com, then immediately downloaded it into another FTM database, they wouldn't be the same. For example, I had a number of saved books in my database, but they were missing in the downloaded database; this is noted in article 5356. I also found that the children of each family were no longer in birth order, even though they were in order in my ancestry.com tree; this is not mentioned in the article 5356. I'd have many hundreds of families to fix in FTM 2012.
I was hoping that support would have a way to repair my corrupted database, but they couldn't do anything with it.
While one might argue that this is the way TreeSync is supposed to work, my basic problem is that when used as intended, it's fragile. One uncontrollable mishap and you stand to lose information, even if you've got a recent backup.