Conveniently Replace Elements in Arrays
Mathematica 6 enhances ReplacePart to allow a convenient syntax for arbitrary index lists with symbolic patterns.
In[1]:=  |  ArrayPlot[
ReplacePart[Rasterize["ABC", "RGBColor", ImageSize -> 50],
Table[RandomInteger[{1, 50}, 2] -> Gray, {500}]]] |
Out[1]=  |  |