I've been playing with an Ipad2 running PDF plates under Goodreader.
Under GR, if you touch the page it should display the page controls which (among other things) enable you to navigate back up one level and select another plate for the same airport, or go back up two levels and select a different airport (if that is how the hierachy is organised).
A lot of the time, it doesn't work. The single-touch gesture doesn't do anything. You have to keep prodding the screen and eventually it notices.
I don't see this issue in other apps.
It is absolutely necessary to be able to rapidly navigate between different plates for an airport. I would thus not want to rely on an Ipad as my only conveniently accessible means of displaying approach plates.