leadslead-
If the manual doesn't specifically prohibit it, then it's OK to do it? I'm finding it personally difficult to buy into that line of reasoning. The manual would have to be many thousands of pages thick, and even then, I think something would be missed. Much safer (from the manufacturer's legal liability standpoint) would be to say what you "can" do, and anything else would be on your head.
Aviation Week, in the aftermath of AA587, has done a number of excellent, eye opening articles on rudder usage. Some of which bring out statements from the structural design engineers saying words to the effect of, "..we never expected the pilots would do that...".
dvt-
If Davies says it's not a good idea, that's good enough for me (and untold thousands of other professional pilots). If you can't learn from him (and others like him), who are you going to learn from?
For what it's worth, my company prohibits slips (to lose altitude) across our fleets. I was part of that decision, and I'm comfortable with it.