Transparent computer screens? Well, no, not really. The images in this Flickr galler are just illusions, created by setting a picture of the environment as the desktop background on the computer.
It would be easy to extend this idea and set up a web cam to stream images of the background to your desktop. It could be full video, but for better performance, I think I'd just prefer using a time delay to keep it current (say, 2 minutes?). That would keep your background up to date with any subtle changes in the background (natural light, movement of objects, etc). Optionally, a motion sensor could be used that would trigger an update every time you tilted your monitor.
Sure, it's nothing but eye candy, but if implemented correctly and efficiently, it could be uber-cool.
UPDATE: One more crazy idea - incorporate two micro-cameras and 3d glasses with a tracking device. This would allow several things. First of all, the objects in the background could really appear to be in the background (and all of your icons/programs/videos could be cooler, too). Also, by monitoring the position of your head in relation to the monitor, the cameras and background image could be shifted to make the illusion of transparency even more complete.
Implementing this would definitely be worth ultra-double bonus points (and probably a PhD).