Just came across it and it looks and works like lightbox but seems to be smaller in filesize and can even show html pages within a fixed sized window. Would be great because I'm trying to use just one (lightbox-)script for Plogger images and for popups within WordPress posts and this would do both :)
Cool stuff. We're actually using Greybox right now inside of Plogger Beta 3 to show the gallery preview in the same window instead of jumping outside of the admin area. I really like the idea of being able to put more than images inside those little windows.
Also, the filesize is a real plus since you don't need Scripaculous and Prototype, just JQuery (which is only 10kb!).
Very Coooool!!! I would like to eliminate the medium thumb and large thumb links in gallery.php and open an html document with thickbox when you click on an image in an album. Does anyone know how and if this is doable.