This enhancement should not be extremely hard to implement and would have a
significant impact on usability of impress for presentations.

THE PROBLEM: 
The slide 'swapping' or 'browsing' in fullscreen is much faster in OO 2.0 now
than it was in 1.1.x, however still slow compared to powerpoint. I mean the
delay when when the sandhour in the left bottom corner is being displayed and
when the next slide is being pre-rendered in the background. The trouble is, you
want, e.g., skip back 5 slides during the presentation to react on a question
from publicum and it takes just too long to get there. If you experienced such
situations you will understand, this is really a trouble.

THE ENHANCEMENT:
I got already some nice proposals during last email conversation with HTH:

> Short-term solution: have a slide navigation menu, where you can directly
> select the slide you want to jump to (please file an enhancedment issue,
> if that's acceptable). Long-term solution: speed up rendering and make
> rendering preemptable (which it currently isn't - the renderer simply does
> not notice that the user has already clicked enough to be four slides
> further).

I think a kind of slide-navigation menu or widget could do the work. However,
one has to find some decent way how that should look like - a pop-up listbox
window showing +5/-5 slide icons or their titles (using UP/DOWN keys and ENTER
to select) ?

But implementing preemptable rendering could be efficient as well and might be
not that complicated. What about checking at least between every object being
rendered for a keypress and quit render process in that case ? Otherwise,
multithreading would be necessary.