I have a 3D stack of tiles that is actually 1 tile with an array modifier creating the instances offset to form a pile. Is there a way to make each instance have it's own random variance in the X and Y axis and in Z rotation so that it is a realistically more chaotic imperfect stack, without me having to "apply" the modifier and manually nudge each tile around? This would be great so that I could adjust the "Count" and each new tile would automatically be randomly slightly different placement than the one below it.
I don't know how to do that and keep it in an array modifier, but here's a workaround: Drop the array and duplicate the tile in the Z direction. Select the tiles you want to randomize, then go to Object > Transform > Randomize Transform. The controls will appear in the toolshelf T.
There was some activity toward improving the existing array modifier in this way a few years ago, but it never got to the trunk.
Here's the story on Blender Nation: http://www.blendernation.com/2012/01/05/advanced-array-modifier/
And here is a build for it on GraphicAll: http://graphicall.org/537
You could model with that, apply the modifier, then continue working in your preferred version.