Chad Seigel, Group Manager for Creative Suite has been quoted as saying, "Adobe is trying to break barriers and integrate all products."
Changes to Photoshop CS4 include an improved interface with the entire application enclosed in the frame which means dual monitor users can have more than one application running. The workspace switcher is for swapping between applications such as Camera RAW 5 and Bridge.
Some welcome improvements include zoom ratio which is less likely to show jagged or pixelated lines and also boasts a flicker free zoom.
You can also now rotate the canvas without jagged lines and the brush size can be previewed on the document. This means that when the tool is placed over the image it can be moved in size and allows you to see it before you use it.