CS4 evaluation

CS4 is an evolution of CS3 but not a radical change.
I like CS4 but so far I fail to see it as an indispensable upgrade, unless you get a new dSLR and Adobe will only support its raw format in its newest version of Photoshop (the Adobe version of "gotcha") The GUI accelerated functions are a first for a commercial program but add liitle to speed or functionality. I hope Adobe will continue to work on tapping the GUI for accelerating parallel processing because processing static images would seem ideal for that.
Changes to the desktop are just changes: I personally fail to see how they improve productivity since I have to change some of the workflow processes that were consistent in the last 4 versions of Photoshop. Those desktop changes are comparable to the arbitrary changes Microsoft and Apple make when the come out with a "new" OS so you will be convinced it is indeed "new".
Rather than unifying the ACR and the desktop Adobe has shovelled more into the ACR that works differently but does the same thing as what is available on the desktop. This forces users to learn arcane and poorly documented procedures for two workspaces within the same program.
Poor documentation remains the bugaboo of Photoshop. If you read different "experts" you will find wildly different explanations of how tools work and how to use them. More than one set of tools visually, and I presume mathematically, can be used to arrive at the same effect. Many tools are difficult to use simply because the naming conventions are unintuitive and non-descriptive, a throwback to the geek/wonk days of computing. The most comparable situation I can think of is how the morons who programmed Vista have named the controls for sharing Vista folders on a network.