Over at Oh Gizmo they are reporting (here) on the showing of a prototype EL display by Japanese company Teraokaseiko that is transparent (for pixels in the "off" state) and that has a touch surface on both sides.
If someone has an interesting idea on how this could be applied to electronic reading, then I'd be interested to hear it - as dual-room tic-tac-toe ("noughts and crosses" for our British readers!) is not high on my list of priorities.
It reminds me (without the need for the dual-sided touch screen) of an idea I had a long time ago and was interested in prototyping: marrying a transparent display with a paper navigation technologyand have a transparent device (a little bit like one of those trekking compasses) that could be slid over a map and that would display (selectable) enhanced information.
You can't put all the possible layers of information on a map and keep it readable, but with this you'd have a basic map and then select whether you wanted roads, tracks, walking paths, hotels, ATMs, bars, shops, tourist info etc etc... and off course the idea could be extended to paper documents to maybe show subsequent edits, metadata, related info etc.
Any more ideas?