I once read someone's post that said if you put a book (or books) from your bookshelf on hold, it/they go to the end of the FIFO line.  Is this true?  I couldn't find an answer in the help docs.  Thanks.

That's what I remember hearing, too, Sassy.  I do know that you can go on Vacation Hold (for your entire bookshelf) without losing your FIFO place, though.

yes, if you use the individual hold on your bookshelf, when you take it off hold that becomes your posting date and it goes to the end of the line.

If you use Vacation Hold then the books maintain their place in line.

Yes.  This is confusing as the Wish List hold lets you move up in the line.  But the book shelf hold removes you from the FIFO line.  You enter back at the end of the line when you re-post your book.  Use vacation hold for your bookshelf.