This works to clean up blemishes and ugly skin on shots with a lot of skin showing. It works because the majority of skin imperfections can be picked up in the blue channel.
- Duplicate your background layer
- Go to the channels palette and select the blue channel by holding command and clicking the mask icon.
- Select the duplicate background layer. Add a mask to the new layer by clicking the Add Mask icon at the bottom of the palette.
- Add a surface blur filter by selecting Filter > Blur > Surface Blur. A smidge will do, but overdo it a little. Adjust it later via the layer opacity setting.