What are common techniques for adding eggs to soup? I have seen different techniques for adding eggs to soups. They seem to be a polarizing topic - I have known people to find the sight of "raggy" soup disgusting, and I have family members who won't eat a clear soup. 

These are the methods I know of, but if you can add to the list, I'd be happy to hear about it. 


yogurt: Mix egg with yogurt, don't overmix/froth. Pour it in one big glob into the prepared soup the moment you remove it from the heat, stir. Should result in very fine grains distributed perfectly throughout the soup, making it opaque. Sometimes results in big rags floating on top instead. 
pure egg: Pour slowly a mixed, slightly frothed egg into the soup while stirring vigorously. Should result in big, spongy rags floating in the clear broth. 
egg and cheese: Mix the egg with finely ground hard cheese (parmesan works best). Slowly drizzle into the broth. Not sure what the perfect result is supposed to look like. 
egg and flour: This is more of a thickener. Slowly pour it after the soup is removed from the heat. Should result in an even, slightly thickened broth with no visible rags and no fat spots swimming on the soup. 
emulsified egg. Emulsify egg with oil (or use mayonnaise or hollandaise) and add it to the soup after it has been cooled to serving temperature. Should result in evenly thickened soup without visible rags. 


All these are used in a usual "meat, broth and veggies" soup, not a pureed soup or something fancy, although I suspect there are egg methods for those too. 

What are the advantages and disadvantages of each method? How do they influence texture, richness, rag size, taste? Are there special conditions under which I should prefer one method above the others? Is there a consensus among cooking professionals for which method is to be used with which kind of soup? 

Edit 

The answers are interesting, but I would like to see more information than a simple list: What type of soup should the method be used with, and why? How does it change taste?
In Poland some soups (notably żurek or a sorrel soup) are served with a hard boiled (separately) egg added.