One of the common questions we get is "will my existing third-party plug-ins work in Photoshop CS5?"
Well, it depends on the manufacturer but most companies will be releasing (if necessary) small updates to make sure their product is compatible.
Here's the first plug-in news that I've seen, from OnOne Software:
"I am pleased to announce onOne Software product support for Photoshop CS5 and Photoshop CS5 Extended. All of onOne's currently shipping Photoshop software plug-ins will be compatible with the new Adobe® Photoshop® CS5 and Photoshop CS5 Extended software announced yesterday by Adobe. Compatibility updates will be made available free of charge to registered owners of the titles listed in the attached release."
More news about plugins as I hear about them.