Where do I look in iTunes to find sync errors?
I had the error again this morning - three items failed to sync.

I do finally have a potential culprit. The presence of App store updates seems to correlate with these errors. It fits all the criteria so far that come to mind. 


temporary and sporadic (most of the time, I'm not in the process of downloading apps while syncing and even with simultaneous downloads, my internet is such that this is generally a 1-10 second window or less per app)
resolves itself without needing user intervention


I've poked at this several times and it doesn't seem to correlate with the sync errors in a pattern that I can detect. 

The only explanation I can guess is that there is no log where these errors are collected.