I'm still not completely sure how this event will work, so my suggestion is maybe not feasible, but here it goes...

I have something for concepting and if there is someone with good coding and probably math skills, we could maybe implement it during the weekend.

I would call it Lightscribe, Lighttalk, Laserwrite or something similar. Basically you enter some text. Then you hold the screen of your device facing away from you over your head in portrait orientation. Now you wave your arm continuously from left to right. If you are in a dark place the formally entered text should be visible as a ghost image readable even from far away.

The idea is of course not mine, there are already devices like that:
http://www.gadzooki.com/cool-stuff/lighttalk-ii/

Still, it could be something pretty neat if the display of the N900 is bright enough. Also it could be something with a little wow-factor which IMO has something to do with positive user experience and which is still lacking on the platform.

We have many good/nice/solid/useful apps, but we're missing out the wow-apps