I'm actually tempted to back to CS3, the CS4 upgrade was expensive and has been terribly unstable for me. After Effects crashes constantly on me, Photoshop crashes fairly often (100% when applying Render Lighting wih a custom omni light), and Illustrator isn't crashy but it's extremely slow, even on a Mac Pro octocore with separate system drive and RAIDed documents drive, especially launch and shutdown.
And all this is happening on 3 different systems (all running 10.5.8). I don't know if Snow Leopard would help but CS3 was much more stable and I miss it.