The iPad app is so useful, but the fact that there doesn't seem to be a way to hide the toolbar at the top of the screen makes me not use it anyways. I need the screen real estate for reading when I'm not annotating.

This doesn't seem like it would be very difficult to add as an option – when autohiding, the toolbar would just be an overlay, so as to not make the page "jump", and a tap on the page would bring it up – just like most other PDF readers.