Adobe Principal Product Manager for Photoshop John Nack reports that the company has put together a Snow Leopard FAQ (PDF) notifying customers that while its Creative Suite 4 package is compatible with Apple's forthcoming Mac OS X Snow Leopard, Creative Suite 3 and other earlier versions have not been tested for compatibility and will not be updated if found to be incompatible.
Apple and Adobe have worked closely together (as always with new OS releases) to test compatibility. As for CS4, everything is good with the exception of auto-updates to Flash panels (which I guarantee you're not using*) and Adobe Drive/Version Cue (which doesn't work at the moment on 10.6). CS3 & earlier haven't been tested.
In response to a reader's comment expressing surprise that Creative Suite 3 had not even been tested, Nack responds that while CS3 almost certainly was tested by Adobe, the company has likely taken a conservative route in its guidance in case users do experience issues with CS3 under Snow Leopard.
I found that really surprising, too, and I'll try to get more info. I'd frankly be shocked if people at Adobe & Apple really hadn't tested CS3 on 10.6. I *think* it's just some corporate conservatism at work here, and Adobe doesn't want to over-promise anything. As I say, though, I'll try to find out more.
Upon further questioning of Adobe's lack of support for Creative Suite 3 on Snow Leopard, Nack points out that limited resources dictate that the company focus on current and future priorities, including customer support and feature development, rather than spending time assessing and modifying software released nearly two and a half years ago to ensure continued compatibility.