I had too much content. Therefore there was a much longer version of the presentation that has been put online here: HHGT FOSS talk slides extended version (SlideShare).
There were actually more resources when I was exploring this:
The entire talk was constructed using a js/jquery tool called shower with a django backend of my own devising which is all online here: elena/hhgt-fossd (actually this is the whole blow-by-blow construction of the talk which is both fascinating and scary to revisit). Which mean that the output is also entirely in html, so I will endeavour to put a static version publicly online. I did some things to the stylings that broke shower in most browsers, but made for a nice finished product, but something we're all just going to live with as I'm not revisiting it (unless I have to) as this presentation took a serious chunk of time to put together which was taken from other projects which I'm now working hard to return.