I ran into a small but rather annoying compatibility issue with Snow Leopard and Photoshop CS4. I'm using a unibody Macbook Pro and after saving an image, I am no longer able to use any of the multi-touch features without restarting PS. Not a huge deal, just annoying..
For some reason, I"m not able to use the multi-touch features at all under CS4 and Snow Leopard. I did a clean install of Snow Leopard and migrated my lastest time machine backup, but completely cleared out CS4, then re-installed (was getting the Licensing error on launch, and a clean install resolved it), but now I'm not able to use any of the multi-touch features... zoom, rotate, even drag.