ACR 4.0 has made a few other minor changes, mostly in the layout of the dialog box, and all designed to give you more space to view your image while making adjustments. The Workflow Options have been removed from the dialog box and are now accessed via a link below the Preview. The link shows what the current selection is, and I find that I very seldom make changes to these settings, so this was a good move in my opinion.
The Histogram has also changed a bit. The Highlight and Shadow Clipping controls, which used to be checkboxes in the Toolbar, have been moved into the histogram itself, but function identically to the previous versions of ACR. You’ll also find basic EXIF data for the selected image in ACR now, with aperture, shutter speed, ISO, and lens info displayed—all helpful if you fine-tune your images based on these settings (you can change the defaults for the way ISO is handled in the Camera Calibration panel).
Finally, a new Full Screen option has been added that toggles the ACR dialog box between normal size and maximized for your screen.