DeepZoom for Powerpoint : pptPlex
That tool refresh the way I'm using Powerpoint for my presentations.
So awesome to use some DeepZoom capabilities. Now, on top of creating your slides, you can focus on the big picture (i.e. the main value of your message) and create a zoomable canvas from where you can zoom to your slides.
Here is the link to download pptPlex.
More information at: http://www.officelabs.com/projects/pptPlex/Pages/default.aspx