Perhaps not quite as slick as you are describing or quite as non-linear but isn't this what Church worship presentation software already does? For example: http://www.zionworx.org.uk/features.htm (not a personal recommendation)
The operator can see a sub-set of the slides and select the next one to be displayed ~ very useful if the worship leader decides to sing the chorus again or jump back to an early verse!
It seems to me that much of the idea behind this, is offered in the PowerPoint addon pptPlex from Office Labs. http://www.officelabs.com/projects/pptPlex/Pages/default.aspx
I've seen it used in a lecture, where the speaker went non-linearly between slide-groups and individual slides.
It's a pretty cool concept - check out the videos on that page.
Actually, take a look at this video: http://www.officelabs.com/Lists/Posts/Post.aspx?ID=78 where you can see pptPlex in action on a tablet PC connected to a projector. Isn't this pretty much what Seth has in mind?
Yes, good point about the pptPlex, but it doesn't look like it will run on an iPhone/iPad device. Correct me if I'm wrong bout that btw.
I also don't believe anyone is somehow saying that non-linear or zoom-in/zoom-out presentations are original ideas. It's just a different twist. When I use to work in the multimedia presentation industry, that stuff was very common.
I remember back in the day, my own presentations were non-linear and zoom-in/zoom-out features consisted of me walking over to the audience and handing them an illustration of what I was talking about.
It uses flash, but this looks like what the core ideas is:
here's one on school:
http://voicethread.com/share/705958/
I've used XMind for presentations - free download, open source
Cross platform - Windows, Mac, Linux and a portable version. Nothing for iPad or Android yet though.
XMind says they are working on an iPad version. I use xmind all the time on multiple platforms. Love it. Great when someone wants a copy and you can get them started for free. All they need to do is set up an account. If they want the paid premium version it is $40. Great value.
I look forward to the xmind version for iPad. That could be my "killer app" reason for an ipad. So far no killer app reason exists for me.
Dave