I have been playing with this new feature all day. It is addictive in its ease of use and powerful adjustment capabilities. According to John Nack, the Targeted Adjustment Tool (TAT) is used “on-image adjustments (i.e. click and drag on a certain color or tonal range to adjust the corresponding values)”

The new tool is located in the menu bar on the top of the Camera Raw window.

The new tool lets you select any part of the image and then click and slide the mouse to adjust the selected area. 

In the following example I clicked on the red vest and moved the mouse to the right to desaturate the red.

Very Powerful stuff.