Some time ago I published Flipr source code:
Rainer Brockerhoff wrote:

…a category on NSWindow to flip from some window to another window.

I’m not sure how many people adopted it, but the nice Karelia folks are using it in the upcoming iMedia browser. A few days ago they asked me to look into a “hesitation” effect which could be seen in the first frames of the animation in certain circumstances, and it’s now fixed… so if you used it somewhere, download it again (and tell me).