Hello!

I spent some time looking at some apps & how they implement full screen.
The important thing i think is that most hildon applications do not implement a scroll bar in the main display area. This leaves the right side of the window free for other uses. Also due to this, a full screen button in the lower right corner looks quite neat.
Scrolling is implemented mostly by swipe, with some exceptions like fbreader, where you touch the upper part of the window to scroll up, and the lower part to scroll down.

This raises the issue of how to select text.
In maemo browser as well as xterm, it is done by entering a 'text select' mode, in which swiping the screen will select text instead of scrolling. You enter this mode by clicking on an arrow shaped icon, like the windows pointer.

Conboy does not have a text select mode. Here you have to select text by using the keyboard. So, swipes for scroll and keyboard for select... though i personally don't like this solution and would rather have a text select icon on the status bar.

So i think for zim, first issue to decide is whether to keep the scrollbar...?
If yes, then i think a simple solution would be to reduce the height of the scrollbar, and vacate some space below, which can be taken up by a full-screen icon. In full-screen mode, only the scroll bar and full screen icon would be visible. When you click the full-screen icon, the status bar would pop up alonside the full-screen icon. The status bar would have the same height as the full-screen icon, so that the full-screen icon now appears part of the status bar. ( pl see screenshots of fbreader)

Re how other apps enter full-screen, it is either by an icon in lower right corner, or an icon on a permanently displayed toolbar, or through a menu which appears by clicking the title bar. (there could be other ways, but for hildonised apps i think these 3 are the standard ones)

I'm attaching some screenshots of Conboy, fbreader & opera mobile on n900. If you want any other screenshots, i will be happy to post... :-)