Keynote uses separate screens for display of presentation and display of presenter's notes. That means if you have the presentation projected to a screen, the secondary display (your laptop) is where the Presenters notes are found. That said, you need some work arounds:
1. Presenter's Notes Fonts and images can be enlarged using Keynote > Play > Customize Presenter's Display
2. Wait for Mountain Lion (next month) - it is supposed to allow AirPlay from your laptop so that you can connect an external monitor to your laptop to mirror your secondary screen to it and send your presentation to an Apple TV device.
3. Use an iPad with Keynote Remote app controlling your laptop via WiFi - you can wander about during your presentation and view your Presenter's Notes close-up while talking and transitioning slides.
Short of that, 3x5 notes are useful and don't require batteries.
Many thanks for your great suggestions. I do already have Keynopte for iPhone and should probably try it on my Ipad as well. I could also try a Mac mini as I believe that suports 2 external displays. However the thing that really intrigues me is that the mouse cursor moves from the primary display to the secondary display as if they were adjacent in the arrangement panel. If this was the case then Keynote would not actually be defining 2 monitors, it would be creating 2 virtual partitions from the graphics card.By using a MATROX, I could then 'resplit' the screen into the 2 partitions and control the 2 different monitors.
Anyhow, I really apprecuate your reply and until Snow Leopard comes out I suspect I'll just have to manage.
The app you need for your iPhone and iPad is Keynote Remote. It synchs with Keynote on Macs and iOS devices to give you the Presenters notes on your iOS device to drive your laptop.
The current version was originally written for the iPhone/iPod Touch and has limitations:
In Portrait you can see the notes section and only the current slide on the iOS device - In Landscape you see the current and next slide, but no notes - odd, but that's what it is - I'm hoping there will be an update when iOS 6 comes out. Until then, you will need to embed a clue in your notes as to what will happen next (build, transition, next slide contents, etc.) Even still, it can be a useful tool for those who wish to wander about.
I'm not familiar with any Mac compatible MATROX products, but looking at the website, it appears as most expand the screen real estate to adjacent screens similar to Mac displays are handled.
I use a Belkin Wye Connector to attach a second display (a cinema display) to my iMac. With that, I can display Keynote on my iMac screen and see the presenter's notes in the adjacent screen, but the choices are to display or not display presenter's notes on alternate view. When turned off - no notes. However, they still appear in Keynote Remote on my iPad. I tend to not rely on notes, so my needs are a bit simpler than yours. As long as I know what's next, I can talk my way through the topic fairly easily.
Again, good luck.