I just (in the last half hour) installed it. The first thing I noticed that I don't like is that 'Bridge' the file browser application, does not flag files with a simple flag. Now it does 'label' files, and I can make labels work like I did Flags, but my work flow used the Flag capability with every shoot I processed.
On the other (things I liked) hand, the curves inside the new ACR is wonderful. Well, at least on first try. I processed three files I had previously converted with the old ACR (2.4) and the resultant files from CS2's ACR (... 3.0?) are finished after conversion. I can go directly to Print, or resize, sharpen and Save for Web without any interveening PS steps.
So now I'm gonna go and work some more images, and try to build back my Raw workflow. By the way, lots of stuff is moved around, and it doesn't automatically get all the old actions and scripts from PSCS.