I have dragged and dropped about 30 png's into a psd document so that they're each in a separate layer but laying on top of each other. I now wonder if anyone knows of a nifty trick or script to distribute these layers so that they're instead ordered in a grid in the document?
The easiest method is to place all the individual images into a folder on your desktop then use
File > Automate > Contact Sheet II... within Photoshop to select the folder of images and have them arranged into a grid for a single document.
I believe the Contact Sheet script may be part of Adobe Bridge for CS6.
If you already have everything loaded as layers, you'll have to manually move, align, and distribute layers. There may be a script somewhere to do this for you, but since the nature of a grid is dependent upon the overall document size, I'm not sure you could find something pre-made which works as well as the Contact Sheet script.