http://www.virtual-laser-keyboard.com/

Yes, pounding your fingertips against a hard desk/table top surface sounds like an enjoyable way to use a computer/PDA....

Seeing as how they aren't pressure activated, I'm not sure pounding is necessary.

Thats pretty cool from a gadget perspective. I wonder how it would feel though, like a table top I realize yes, but there's something to be said for the tactile sensation of a keyboard when you're hammering away.

This would kick ass for PDAs.

That sounds like something out of Star Trek, or any of the other futuristic movies. I know there's one in particular that has 3-d computer images that they use, but its name is eluding me at the moment. Would be really handy for laptops I imagine, or anything else that does not really have a comfortable keyboard to use.

http://www.laser-magic.com/HoloMirror_360/HoloMirror_360.htm

My company has actually rented one of these for a conference, really neat toy and it was simple to setup and use. Just don't have that kind of cash laying around for a personal toy.