I have been researching the interaction between water and surfactants. I have a few points where I cannot seem to complete my thoughts so I will tell what I know, and ask what I don't:

I understand that the Calcium and Magnesium ions present in all types of water (hard to soft) will eventually react with soap (or more technically, salt). This is because the Ca and Mg ions in the water have a stronger charge (+2) than the Sodium or Potassium (+1) that was used to make the soap. The Ca and/or Mg ions replace the Na or K, to form another type of soap (or salt), that we commonly refer to as "soap scum." There are chelating agents, such as Tetrasodium EDTA, that are added to commercial soap to somewhat negate this transfer of ions, but sometimes it doesn't work (Ref).

I also know that synthetic detergents work better in hard water because they are structurally different than soap, and do not react with the Calcium and Magnesium ions present in water (Correct me if I am wrong). I have also read that some syndets are affected by the presence of acids in water (Ref). 

Q1: If both soap and some synthetic detergents are anionic, why do they behave so differently in hard water? Are there any cases where a syndet would not perform well in hard water? What about the claim about acidic water?

Assuming that one is using a true soap or a combination bar, and Ca or Mg salts (soap scum) is being formed, is this a problem for the skin? Some seem to think so (Ref). There have been accounts on the Beauty Brains site of people experiencing buildup on their hair, but I have not seen anything about skin. From what I know from cleaning my shower, it seems like it could be just as easily deposited on the skin.

Q2: Can soap scum residue be left on the skin even after rinsing? If so, is this a problem?

Finally, I wouldn't mind hearing your critique of the recent Dove commercials, particularly the "sciency" ones claiming: "Soap leaves scum. Dove doesn't." There was a small experiment debunking some of the claims in the video on another site, and they seem to conclude that Dove is no different from other soaps when it comes to hard water. (Ref)

Q3: Anecdotal evidence aside, does Dove truly preform better in hard water? If so, how is their formula any different from other combination bars, that also contain chelating additives?

Thanks for your help! Please feel free to correct/inform my thinking anywhere it is off. There are just so many websites with information that isn't complete! Give me the unabridged version please! ;D

-Wade G.