Photoshop CS4 panels will not be compatible with Photoshop CS5. Not really all that unexpected. Also, not all that hard to make CS5 versions.

They load OK in CS5. It's just that the plumbing has changed that ties together everything between Flex and Photoshop.

Hey, lots of new features also means new software libraries. It should not be a major overhaul, although CS5 offers more possibilities for user interaction. For example, things like callbacks and menus.

What's a callback? Well, if you ever noticed that the CS4 (and CS5) adjustments panel change, depending on whether a photo is open in Photoshop, that happens through a callback. It's a programming hook that lets you tell Photoshop that you want to know when certain events happen, like a file being opened. Then your panel can react accordingly.

Callbacks were supposed to work in Photoshop CS4 and didn't (reliably, anyways). I sure tried.

Also, I'm excied about some new CS5 features that have CS5 panel promise. Improved noise reduction and better edge mask generation, for example.