It looks like, that in CS6 the Crop Tool you can no longer set the PPI - Is this so?
If so, who on Earth made that decision, it was real time saver. This would effect me to the extent I'll go back to CS5 as I'm using this feature quite a lot. Pity because CS6 has some nice features.
When the crop frame with black handles is visible (e.g. after clicking on the image with Crop Tool), press R key for a dialog where you can enter resolution.
The PPI can be set in Photoshop 13.0 - it's just done a bit more indirectly, by choosing Size & Resolution from the drop-down menu. You can make it a bit more direct by defining a preset, assuming you use the same values over and over.
Direct 3 box operation of the Crop tool has been restored in the 13.1 version Cloud subscribers have just received...