This plugin has just been updated to version 1.1 ... it now allows transparent backgrounds, non-circular dots, overlapping dots and variable sized dots.
See what you think!
Edit: Here are a couple of examples ...
The top image is the same as in the first post, using dot size 2.33, size variation 0.27, spread 0.54, squash 0.45, bias 0.0 and lightness threshold 0.97. The darker areas are due to the "squash" value.
The bottom image uses variable sized, non-circular dots.