Hi Carsten

I've been using org-mode to create a few presentations and found it to
be extremely productive. I use different levels for parts (in the past),
sections and subsections. Beyond that I just use lists. I haven't used
blocks and columns (probably because it wasn't easily possible so far).

Also I use separate org files for all presentations.

See
http://www.daisy2009.de/files/presentations/itc/egli__daisy_producer.pdf,
http://liblouis.googlecode.com/files/liblouisSlides.pdf and
http://liblouis.googlecode.com/files/liblouisSlides.org for examples

Here's the relevant expert from my .emacs