I've tried out the beta version and to be honest there doesn't seem to be that much that's different from CS2 - certainly not in the areas that are relevant to the bulk of my Photoshop activity. The improved Camera RAW tool might be useful, and maybe the updated version of Bridge (if I didn't already have Lightroom) and the new Filter Adjustment Layers will be useful for fans of non-destructive editing.
Anyhow, here's an overview of the new features by
PS guru Scott Kelby:
A Quick Look at the New Features in Photoshop CS3, Public Beta Preview | Photoshop User - NAPP