Holy shit, this really works!
Courtesy of kottke.org (whose coolness I only recently came to appreciate):
To view the images in 3-D, cross your eyes until a composite image forms in the middle (it even works with the thumbnail above). From what I’ve read, a small percentage of you (5-10%) won’t be able to see the effect, so if you can’t get it to work, that might be why.
It took me a dozen times crossing my eyes to make it work right—but now that I understand how to do it, it is such a fascinating effect! The trick seems to be, first, to cross your eyes enough to perfectly overlap the two images. Don’t worry that it’s still blurry. Then, let your eyes relax and slowly focus on the scene. In a few seconds (for me, anyway), the stereograph will focus and pop out.
It’s almost as cool as those black-and-white stereographs you find in the antique stores. Maybe even cooler, since it doesn’t require extra equipment. (Or does it now…?)
Edit: Turns out this is the same concept used by those damned Magic Eye 3D illusions. Well, shit. If someone would have just *told* me to cross my eyes and look at it, I might not have spent ten years looking for the damn sailboat.