With the release this month of CS6 and ACR 7, which matches the raw engine in Lightroom 4, ACR has made a considerable change. Modifications to the way the raw engine handles many aspects of a raw file as it enters the system are considerable, and in my estimation, very good. I have long been an advocate of modifying the camera raw defaults to favor lower contrast and less aggressive black points to begin the processing of images. The new ACR 7 does exactly this, using a linear rather than a jpg like curve for handing you the initial processing of the image. The result is better low end detail rendering and more control over tonal range.
The new sliders in the default tab will take a little getting used to at first, but you will soon realize that they are much more logical than before, and offer a lot more subtle control, especially at the end points. Highlight control in particular is improved. I never cared for or used the Recovery slider much as it simply appeared to gray out the high values. The newer Highlights control is less aggressive, and far better at recovering high end details without flattening out the higher values. Similarly, the new Shadows slider is less aggressive, but as good or better than the older Fill Light slider in pushing information into the lower end values without mushing up the bottom.
The Exposure slider is more intuitive than before, doing exactly what you would expect it to do in raising mid tone values, which is how most people would tend to use it. At the same time it does less to set the white point than the older version. It acts more like the previous Brightness slider in that respect. The new Whites slider is more accurate at setting the white point, and does so with minimal effect on the mid-tones. The Black slider will confuse some people who were accustomed to seeing the blacks get darker as you cranked it up. Now it is set to zero to start and can be moved in both directions to increase or decrease the black point. To make things darker now requires lowering the numbers instead of increasing them. Again, this is a more logical setting technique.
The sliders do nothing for color, as before, so setting the white/neutral balance of the image still requires using the White Balance tool. However, the Tone Curve panel Point settings now include individual color channels. I suspect most people will miss this important change which essentially allows you to apply curve corrections to a raw file in the individual channels as you would do in Photoshop previously. I strongly suspect this was in answer to giving curves control to Lightroom users as the change is the equivalent thereof. Using this with resetting raw defaults can be used to take bottom end color casts out of raw captures. Similarly, presets can be used in ACR or Lightroom to make these changes easier and speed up image processing.