Dates don't seem to be zyncing correctly, but text fields are. What's going on?
The scripts in GoZync represent all your data as "text" in the document we pass back and forth. Converting dates to and from text is the only place where FileMaker fails to respect "Use System Formats". In these cases FM uses the date format initialized when the file was created: if your file was created with UK dates, for example, it will conflict with GoZyncs file which were created with US dates.
Fortunately this is easy to fix. Cloning a file (Save a Copy As / Clone) wipes this date information and resets it using the format of the machine which next opens the file.
So making a clone of GoZyncConnector and Mobile (if you're using ours) should get you sorted. There is data in both files you'll still need, however. So after cloning, renaming, and opening you're new files, you'll want to import data from the uncloned versions into the following tables:
GoZyncConnector: GoZync and Interface Mobile: PortalRows, GoZync, and Interface