It's currently in FAQ 40 on horizontal scrolling and entries out of order, but I think it belongs somewhere else. It's debatable whether it needs its own FAQ, but the people who want to use LJ on mobiles/dial-up aren't going to see it in FAQ 40 and are unlikely to see it in FAQ 6 since they may not be posting images.
Edit: After thinking about this further, I think we could use a new FAQ for dial-up / mobile / disabled users to show how they can use built-in features to reduce bandwidth and/or screen size and increase accessiblity. A related accessibility request is http://www.livejournal.com/support/see_request.bml?id=536026 with some interesting commentary in http://www.livejournal.com/community/lj_style/327262.html
This FAQ (Can I use LiveJournal with a slow connection or mobile device? How can I make LiveJournal more accessible?) would contain:
*"Mobile View" friends group http://www.livejournal.com/community/changelog/2545556.html
*"Default View" friends group
*a list of simpler styles & link to FAQ 7 on making custom styles
*voice posts & email posts?
*comments via email