This is not something I have written, but is information that I find very useful.  I have posted the rough idea here in an attempt to preserve it so I don't lose it.  Basically, the following information is designed to dispel the myth that one must use a certain amount of priming sugar every time you brew.  For example, often recipes call for 3/4 cup of corn sugar at bottling time.  This amount, however, may not provide the correct carbonation level for the particular style of beer that is being brewed.  I found the following information that was compiled by Andy Davison of the rec.crafts.brewing newsgroup from research done by Brew Your Own (BYO) magazine's Technical Consultant Ashton Lewis.  Ashton says:

When I was in graduate school at Davis, I derived a simple equation beginning with the ideal gas law and the stoichiometric conversion of glucose to ethanol and carbon dioxide.  The only flaws with the equation are that the ideal gas law represents an "ideal" gas (not a real gas) and glucose is not 100% converted to ethanol and carbon dioxide.  Those are picky points, however.

(1096.825)*(desired volumes CO2)*(liters beer)=grams
 (Serving temperature in ^oK)

For example, we want to prime 20 liters (5.2 gal) of beer to increase the CO2 content from ~1.0 volumes to 2.0 volumes at a serving temperature of 4 ^oC (39 ^oF).  It is key to recognize that beer, even held at atmospheric pressure, is not devoid of CO2 after fermentation, thus the starting volume of ~1.0 in this example.  We want to add enough sugar to provide a change of 1 volume CO2 to the beer.  The serving temperature in ^oK is used because it is in the ideal gas law.  (^oK= ^oC +273).

(1096.825)*(1 volume change)*(20 liters)=79 grams
        (277 ^oK)

By using the above equation, one can more accurately determine the proper amount of priming sugar to add to a beer in order to obtain a particular carbonation level at a particular serving temperature.

Conversions for Using Priming Elements Other than Corn Sugar:

                     Apparent       Real        Grams
Primer             Attenuation  Attenuation   per liter
Cane Sugar             100%         100%         3.8
Corn Sugar             100%         100%         4.0
M&F DME                 75%          60%         6.8
Northwestern DME        70%          56%         7.2
Laaglander DME          55%          44%         9.3

Table of Common Carbonation Levels:

Beer style               Volumes CO2
British-style ales        1.5 - 2.0
Porter, stout             1.7 - 2.3
Belgian ales              1.9 - 2.4
European lagers           2.2 - 2.7
American ales & lagers    2.2 - 2.7
Lambic                    2.4 - 2.8
Fruit lambic              3.0 - 4.5
German wheat beer         3.3 - 4.5

Solubility Levels of CO2 in Beer at Atmospheric Pressure:

Temp (degC)    Vol. CO2      Temp (degF)    Vol. CO2
       0        1.7             32            1.7
       2        1.6             35            1.6
       4        1.5             40            1.45
       6        1.4             45            1.3
       8        1.3             50            1.2
      10        1.2             55            1.1
      12        1.12            60            1.0
      14        1.05            65            0.92
      16        0.99            70            0.85
      18        0.93            75            0.78
      20        0.88
      22        0.83
 

Bibliography
Ashton Lewis -- BYO Technical Consultant
Andy Davison
Mark Hibberd