To my dismay... yes I say "dismay" because I was hoping it would be coming next year thus allowing me to go forth with my plan to get certified in CS3 this winter... CS4 will be coming out in October from what I hear.
One of the new enhancements I seen is the ability of Photoshop to use graphics display cards for improved speed with larger images. Reportedly, a person was able to work with 443 megapixel images in CS4
PS like it was a 5 megapixel image. Quick transitions, scrolling and such. This is interesting.
However, this could also set Mac users on fire IMHO as Mac computers typically are a little behind in video card technology. The offerings for upgrades for Macs I have seen leave two choices (256mb and 512mb) and both cards seem to either be flakey or lack longevity and tend to die after a year of use. (I think I got this info from reviews at the Apple store actually).
Windows users have long had more video card options mostly due to more drivers that were developed for Windows systems. I still believe many of the better video cards could probably work on a Mac if drivers were developed.
So... I look forward to seeing CS4 even though it will screw my career plans up a little. I do wonder if my current 128mb ATI of current will be of much help to take advantage of this new display technology in CS4 though. Will be researching this more as I find more info.
Start saving your money for October!