Massive thanks Steven58!! You don't want to know how long I spent searching the web and reading posts until I found this.
Like the OP, I had to use the power control widget to turn auto-sync back on. Prior to that I could go to Settings --> Accounts --> Google Account, but there were no checkboxes there. For each item (books, contacts, mail, and calendar) it just said something like 'Press to sync now.'
For future reference, do you know if there's a setting to turn on/off the auto-sync functionality without having to use the widget? Just curious and thanks again!