The thread Lisa Peters (aka: OhThatGirl2001) started way back in about March 2002 describing a pencil sketch method she discovered at About.com was probably the one that resulted in the creation of the Photo-based Art forum, something for which many (including myself) will always be grateful. 
This is a summary of the steps Lisa shared:
- - - - - - - - - - -
1. Background: Duplicate image ("A. Desaturated")
2. "A": Desaturate
3. "A": Duplicate image ("B. Color Dodge")
4. "B": Set blend mode to Color Dodge and Invert (CTRL + I). Don't panic. Screen will go almost (or completely) white.
4a. Optional step: Some methods suggest setting the opacity to 95%. Your call.
5. "B": Filter > Blur > Gaussian Blur - blur to taste.
6. Create a new Levels adjustment layer ("C. Levels")
7. "C": Adjust the contrast by moving the Left slider toward the right. Might have to move the R slider towards the left a bit. Experiment. (Note: Some people prefer to use a Brightness / Contrast adjustment layer here instead.)
- - - - - - - - - - -
Optonal steps to add kind of a pastel-like look:
8. If/when you like what you see, create a new layer "D. Base".
9. Cool Trick. "D.": ALT + CTRL + SHIFT + E (this merges all visible layers into layer D without collapsing the individual layers in case you need them again later.
10. Create a Brightness / Contrast adjustment layer above layer D. Make no adjustments at this time. Name it "E. B/C"
11. Click the Background layer and duplicate it.
12. ALT +CTRL + SHIFT + ] (Right bracket) - to move the duplicated Background layer to the top of the layer stack.
13. New layer name: "F. Color"
14. "F": Set blend mode to Color.
15. "E": Open the Brightness / Contrast adjustment layer; start by moving the Contrast slider to the left. See the soft color appear? Tweak the Brightness / Contrast sliders to suit.
VARIATIONS
---------------
* Adjust opacity of layer F
* Turn off layer E

This is a summary of the steps Lisa shared:
- - - - - - - - - - -
1. Background: Duplicate image ("A. Desaturated")
2. "A": Desaturate
3. "A": Duplicate image ("B. Color Dodge")
4. "B": Set blend mode to Color Dodge and Invert (CTRL + I). Don't panic. Screen will go almost (or completely) white.
4a. Optional step: Some methods suggest setting the opacity to 95%. Your call.
5. "B": Filter > Blur > Gaussian Blur - blur to taste.
6. Create a new Levels adjustment layer ("C. Levels")
7. "C": Adjust the contrast by moving the Left slider toward the right. Might have to move the R slider towards the left a bit. Experiment. (Note: Some people prefer to use a Brightness / Contrast adjustment layer here instead.)
- - - - - - - - - - -
Optonal steps to add kind of a pastel-like look:
8. If/when you like what you see, create a new layer "D. Base".
9. Cool Trick. "D.": ALT + CTRL + SHIFT + E (this merges all visible layers into layer D without collapsing the individual layers in case you need them again later.
10. Create a Brightness / Contrast adjustment layer above layer D. Make no adjustments at this time. Name it "E. B/C"
11. Click the Background layer and duplicate it.
12. ALT +CTRL + SHIFT + ] (Right bracket) - to move the duplicated Background layer to the top of the layer stack.
13. New layer name: "F. Color"
14. "F": Set blend mode to Color.
15. "E": Open the Brightness / Contrast adjustment layer; start by moving the Contrast slider to the left. See the soft color appear? Tweak the Brightness / Contrast sliders to suit.
VARIATIONS
---------------
* Adjust opacity of layer F
* Turn off layer E
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