|Absolutely my least favourite|
At least in theory, these all have the same fonts installed on them, so when the file gets opened on a different machine, I don't get Pages little ''This document may look different' dialog.
Except that somewhere, one of my machines somehow has "Segoe UI" installed rather than "SegoeUI"... which as far as I can tell are identical fonts apart from a space in the name. And if I'm in a hurry and miss the warning dialog, the font (which is the main font for all the body text) gets replaced with Helvetica and completely b****ers up the text formatting and diagram and table layouts. Especially if I then save it and fail to notice for several versions.
I've finally been bitten by this once too often. Guess what I've been doing this evening :D