Usually sync failures are just a temporary network glitch. If it persists, let me know. If you hit Ctrl+Shift+D, you can get a little more info about the errors.
After trying to sync and failing, hit Ctrl+Shift+D and copy the log (or at least the end of it), it gives info on why the sync failed. My saves seem to be syncing without trouble.
Actually, I think I have an idea. There's a 10 second timeout on syncing... so for really long saves (on slower internet connection) it will time out. I'll up that timeout to 30 seconds.