My suggestion is something small, although I imagine it would be rather useful to the masses. I suggest that the save/cancel buttons on all the pages in ACP that require editing something, be placed at the top and bottom of the pages.
Many times I've found myself changing something that's at the top of the page, as most devs (including the XF team) put majority of the important things at the top of the page. Although most of the time the changes are on long pages of either settings, or a template edit, ect. So you're always stuck having to scroll down the screen for a quick change.
Again, small suggestion. The buttons would fit up at the top and not mess up any styling, plus this would be a change that I'm sure no one would hate or want changed back. As it would only serve to help simplify things for them in the backend of the forum.
Not sure if this has been suggested before either. I did search a few times and found nothing, so sorry if it has been suggested before.