I saw a site w/ abt. 20 pictures like this a week or so ago. It spurred me to create my own. I've only done a couple now, but for all you photoshop people (like me), its pretty easy. Just get some sort of background pic, and get a pic of whatever you want to "clear" the screen on. Then put the Background pic on a layer behind the laptop, select the laptop screen and export it to it's own layer, then just set the blending options to make the screen disappear to the amt. that you want. The toughest part is getting the icons to still look sharp.
Great job on your pic by the way! its one of the better one's that I've seen.