I just saw this posted on usenet, got me to trying different things. Kind of fun:

Open Image

Duplicate Background layer

Convert to Grayscale
* Image > Adjustments > Desaturate -or-
* Image > Adjustments > Channel Mixer (set to Monochrome)

Duplicate BW layer

Invert Duplicate Layer (Ctrl + I)

Set Duplciate Layer mode to Dodge - should go white

Experiment with one of the following:
* Gaussian Blur
* Motion Blur
* Noise > Dust and Scratches

Optional: Copy Background again and move to the top of the layer stack. Experiment with blend modes.

(thanks to lmulli)

I tried other filters besides these. Unpredictable, but like I said, fun :)