Guys, I found this on another forum:
QUOTE
Step 1. Choose any Photo Album in your library
Step 2. For Display Style, select the third option (Mosaic)
Step 3. Let Mac OS X optimize your photos for this screensaver
Step 4. Press test and watch it go through a full cycle... watch it for like 3 minutes.

For a second I thought it was weird how a lot of pictures were doubled, etc... but once you see the end result. Awesome! Gogogo core animation

From Macrumors Forum

Best screensaver on leopard, ever! Especially when you're into photography.