Okay, I'm "popping in" about the sugar => more bubbles thing. Makes me feel a little like Mary Poppins!
A couple of definitions:
Soap film = a very thin sturdy layer of soap and water and possibly other ingredients.
Soap bubble = a spherical soap film that encloses a certain volume of air.
The lifetime and size of a soap bubble depends on
(1) the strength and elasticity of the soap film itself which depends on the ingredients in the soap solution,
(2) the rate of evaporation of water out of the soap film,
(3) the presence of contaminants such as dirt or fat, and
(4) the rate of drainage of water in the soap film toward the bottom of the bubble due to gravity.
To make long lived bubbles, you would want to make a relatively strong elastic soap film, slow the evaporation of water, and minimize contaminants in the soap film.
What does a sugar solution or glycerin contribute toward this goal? Up to a point, these ingredients will reduce water evaporation and increase the soap film strength. If too much sugar or glycerin is added, they will cut lather, however, because they will increase the viscosity (thickness) of the soap solution too much. If the soap solution is too thick and syrupy => few or no bubbles. So don't get carried away!
And, since I cannot resist the temptation to expand on this topic....
Castor adds ricinoleic acid to a soap recipe. Ricinoleic acid is an unusual fatty acid because it is somewhat water soluble -- more so than any other fatty acid normally used in soap making. As others have pointed out elsewhere on SMF, castor added to a soap recipe can add bubble-age, even though a pure castor soap doesn't bubble much. This partial water solubility is probably the reason why -- castor soap acts a bit like glycerin or sugar to make a more stable soap film when part of a mixed soap.
The composition of the soap itself contributes to the strength of the soap film. Lower molecular length soaps (such as those in coconut oil soap) tend to make bigger bubbles that pop easily, all other things being equal. Longer molecular length soaps (such as tallow soap or olive oil soap) make smaller bubbles that stick around. My guess is that the longer soap molecules are stronger, so they are able to make a longer lived, more elastic soap film. The downside to being stronger and more elastic is that the soap film is not able to form bigger, fluffier -- and less stable -- bubbles. The amount of saturated fats vs unsaturated probably affect this too, but don't quiz me on this.
Contaminants, such as high superfat, high amount of botanicals, clays, some additives, etc., will tend to reduce the total amount of lather as well as the size of the bubbles, because these ingredients can reduce the strength of the soap film. Contaminants added to an existing soap bubble can "damage" the soap film, much like poking a hole in a balloon -- think about how touching a soap bubble with a dry finger causes it to pop or spraying alcohol on a soap foam will "break" the foam.
http://en.wikipedia.org/wiki/Soap_bubble
http://mysite.du.edu/~jcalvert/phys/bubbles.htm
http://www.mne.psu.edu/cimbala/Learning/Fluid/Fluid_Prop/fluid_property.htm
Edit: See Amathia Soapworks "Lather Lovers Test":
http://www.flickr.com/photos/amathiasoapworks/6878711296/in/set-72157629324839760/
