Just been updating some photos on my home iPad and discovered that a lot of them weren’t syncing.  Very annoying!  After much Googling and poking around in preference files, I decided to try syncing a small iPhoto event across and seeing which ones didn’t sync.  It turned out that some of my photos didn’t have a title (‘untitled’) and it was these photos which weren’t syncing.  After a quick Photos>Batch Change and then changing the title to the filename, this seemed to fix the problem.  Phew!