I have 2 trees linked to Ancestry. One with about 3000 persons and one with about 24,000 persons and several people invited as editors online. Which means they are making changes. Everything works as intended. In the first release there were reliability problems that have disappeared with the numerous updates. We now can keep complete backups on our desktop that will restore and relink to the AMT so with regular backups so there shouldn't be much risk of catastrophe.
It seems like most of the synching problems are now by those who have purchased 2012, imported their data files and synched for the first time. I think this probably has to do with data integrity with their old files that have been built over many years and many versions of FTM. While not perfect, the program performs well for me with no lost data.